Light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

Emission efficiency of a light-emitting element is improved. The light-emitting element has a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a first light-emitting layer and a second light-emitting layer. The first light-emitting layer includes a fluorescent material and a host material. The second light-emitting layer includes a phosphorescent material, a first organic compound, and a second organic compound. An emission spectrum of the second light-emitting layer has a peak in a yellow wavelength region. The first organic compound and the second organic compound form an exciplex.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/725,026, filed May 29, 2015, now allowed, which claims the benefit offoreign priority applications filed in Japan as Serial No. 2014-112448on May 30, 2014, and Serial No. 2014-241137 on Nov. 28, 2014, all ofwhich are incorporated by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a light-emittingelement in which a light-emitting layer capable of emitting light byapplication of an electric field is provided between a pair ofelectrodes, and also relates to a light-emitting device, an electronicdevice, and a lighting device including the light-emitting element.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specifically, examples of the technicalfield of one embodiment of the present invention disclosed in thisspecification include a semiconductor device, a display device, a liquidcrystal display device, a light-emitting device, a lighting device, apower storage device, a storage device, a method for driving any ofthem, and a method for manufacturing any of them.

BACKGROUND ART

In recent years, research and development of a light-emitting element(organic EL element) which uses an organic compound and utilizeselectroluminescence (EL) have been actively promoted. In the basicstructure of such a light-emitting element, an organic compound layercontaining a light-emitting substance (an EL layer) is provided betweena pair of electrodes. By voltage application to this element, lightemission from the light-emitting substance can be obtained.

A light-emitting element in which an organic compound layer is between apair of electrodes is referred to as an organic electroluminescenceelement, and a light-emitting device including the light-emittingelement is referred to as an organic electroluminescence device. Theorganic electroluminescence device can be used in a display device, alighting device, and the like (see Patent Document 1, for example).

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2012-186461

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to improveemission efficiency of a light-emitting element. Another object of oneembodiment of the present invention is to provide a novel semiconductordevice, a novel light-emitting element, or a novel light-emittingdevice. Note that the descriptions of these objects do not disturb theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a light-emitting element inwhich an EL layer is between a pair of electrodes. The EL layer includesa first light-emitting layer and a second light-emitting layer. Thefirst light-emitting layer includes a fluorescent material and a hostmaterial. The second light-emitting layer includes a phosphorescentmaterial, a first organic compound, and a second organic compound. Anemission spectrum of the second light-emitting layer has a peak in ayellow wavelength region. The first organic compound and the secondorganic compound form an exciplex.

In the above structure, it is preferred that the second light-emittinglayer include one phosphorescent material.

In any of the above structures, it is preferred that energy betransferred from the exciplex to the phosphorescent material.

In any of the above structures, it is preferred that a singlet excitedlevel of the host material be higher than that of the fluorescentmaterial and a triplet excited level of the host material be lower thanthat of the fluorescent material.

In any of the above structures, it is preferred that a triplet excitedlevel of the host material be lower than those of the first organiccompound and the second organic compound.

In any of the above structures, it is preferred that the firstlight-emitting layer and the second light-emitting layer include aregion where the first light-emitting layer and the secondlight-emitting layer are in contact with each other.

In any of the above structures, it is preferred that the firstlight-emitting layer and the second light-emitting layer include aregion where the first light-emitting layer and the secondlight-emitting layer are separated from each other, in which case amixed layer of a hole-transport material and an electron-transportmaterial is preferably provided between the first light-emitting layerand the second light-emitting layer.

In any of the above structures, it is preferred that the secondlight-emitting layer be over the first light-emitting layer.

Another embodiment of the present invention is a light-emitting deviceincluding the light-emitting element with any of the above structures,and a transistor or a substrate.

The light-emitting device in this specification and the like includes animage display device that uses a light-emitting element. Furthermore,the light-emitting device may be included in a module in which alight-emitting element is provided with a connector such as a flexibleprinted circuit (FPC), a module in which a light-emitting element isprovided with an anisotropic conductive film or a tape carrier package(TCP), a module in which a printed wiring board is provided at the endof the TCP, or a module in which an integrated circuit (IC) is directlymounted on a light-emitting element by a chip on glass (COG) method.

Another embodiment of the present invention is an electronic deviceincluding a light-emitting device with the above structure and anexternal connection port, a keyboard, an operation button, a speaker, ora microphone. Another embodiment of the present invention is anelectronic device including a module with the above structure and anexternal connection port, a keyboard, an operation button, a speaker, ora microphone. Another embodiment of the present invention is a lightingdevice including a light-emitting device with the above structure and ahousing.

According to one embodiment of the present invention, emissionefficiency of a light-emitting element can be improved. According to oneembodiment of the present invention, a novel semiconductor device, anovel light-emitting element, or a novel light-emitting device can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are schematic cross-sectional views illustratinglight-emitting elements of one embodiment of the present invention;

FIGS. 2A and 2B show correlations of energy levels in light-emittinglayers;

FIG. 3 shows a correlation of energy levels in light-emitting layers;

FIGS. 4A and 4B are schematic cross-sectional views illustratinglight-emitting elements of one embodiment of the present invention;

FIG. 5 is a schematic cross-sectional view illustrating a light-emittingelement of one embodiment of the present invention;

FIGS. 6A and 6B are a top view and a cross-sectional view, respectively,illustrating a light-emitting device of one embodiment of the presentinvention;

FIGS. 7A and 7B are cross-sectional views illustrating light-emittingdevices of one embodiment of the present invention;

FIG. 8 is a cross-sectional view illustrating a light-emitting device ofone embodiment of the present invention;

FIGS. 9A and 9B are cross-sectional views illustrating light-emittingdevices of one embodiment of the present invention;

FIGS. 10A and 10B are cross-sectional views illustrating light-emittingdevices of one embodiment of the present invention;

FIGS. 11A and 11B are a block diagram and a circuit diagram,respectively, illustrating a display device of one embodiment of thepresent invention;

FIG. 12 is a perspective view illustrating a display module;

FIGS. 13A to 13G each illustrate an electronic device;

FIG. 14 illustrates lighting devices;

FIGS. 15A and 15B are schematic cross-sectional views illustratingelement structures of light-emitting elements of Examples 1 to 3;

FIGS. 16A and 16B show current density-luminance characteristics andvoltage-luminance characteristics, respectively, of light-emittingelements of Example 1;

FIGS. 17A and 17B show luminance-power efficiency characteristics andluminance-current efficiency characteristics, respectively, oflight-emitting elements of Example 1;

FIG. 18 shows emission spectra of light-emitting elements of Example 1;

FIGS. 19A and 19B show current density-luminance characteristics andvoltage-luminance characteristics, respectively, of a light-emittingelement of Example 2;

FIGS. 20A and 20B show luminance-power efficiency characteristics andluminance-current efficiency characteristics, respectively, of alight-emitting element of Example 2;

FIG. 21 shows an emission spectrum of a light-emitting element ofExample 2;

FIGS. 22A and 22B show current density-luminance characteristics andvoltage-luminance characteristics, respectively, of a light-emittingelement of Example 3;

FIGS. 23A and 23B show luminance-power efficiency characteristics andluminance-current efficiency characteristics, respectively, of alight-emitting element of Example 3;

FIG. 24 shows an emission spectrum of a light-emitting element inExample 3;

FIG. 25 is a schematic cross-sectional view illustrating an elementstructure of a light-emitting element of Example 4;

FIGS. 26A and 26B show current density-luminance characteristics andvoltage-luminance characteristics, respectively, of light-emittingelements of Example 4;

FIG. 27 shows emission spectra of light-emitting elements of Example 4;

FIG. 28 shows luminance-external quantum efficiency characteristics of alight-emitting element 11 of Example 5;

FIG. 29 shows an emission spectrum of a light-emitting element 11 ofExample 5;

FIG. 30 shows reliability of a light-emitting element 11 of Example 5;

FIG. 31 shows luminance-external quantum efficiency characteristics of alight-emitting element 12 of Example 5;

FIG. 32 shows an emission spectrum of a light-emitting element 12 ofExample 5; and

FIG. 33 shows reliability of a light-emitting element 12 of Example 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below withreference to the drawings. Note that one embodiment of the invention isnot limited to the description given below, and various changes andmodifications can be made without departing from the spirit and scope ofthe invention. Therefore, one embodiment of the present invention is notinterpreted as being limited to the description of the embodimentsdescribed below.

Note that the position, the size, the range, or the like of eachstructure illustrated in drawings and the like is not accuratelyrepresented in some cases for simplification. Therefore, the disclosedinvention is not necessarily limited to the position, the size, therange, or the like disclosed in the drawings and the like.

Note that the ordinal numbers such as “first” and “second” in thisspecification and the like are used for convenience and do not denotethe order of steps or the stacking order of layers. Therefore, forexample, description can be made even when “first” is replaced with“second” or “third”, as appropriate. In addition, the ordinal numbers inthis specification and the like are not necessarily the same as thosewhich specify one embodiment of the present invention.

In describing structures of the present invention with reference to thedrawings, the same reference numerals are used in common for the sameportions in different drawings in this specification and the like.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances in this specification andthe like. For example, the term “conductive layer” can be changed intothe term “conductive film” in some cases. Also, the term “insulatingfilm” can be changed into the term “insulating layer” in some cases.

In this specification and the like, a fluorescent material refers to amaterial that emits light in the visible light region when the level ofthe lowest singlet excited state (S₁ level) relaxes to the ground state.A phosphorescent material refers to a material that emits light in thevisible light region at room temperature when the level of the lowesttriplet excited state (T₁ level) relaxes to the ground state. That is, aphosphorescent material refers to a material that can convert tripletexcitation energy into visible light.

In this specification and the like, blue light has at least one peak ofemission spectrum in a blue wavelength region of greater than or equalto 420 nm and less than or equal to 480 nm, green light has at least onepeak of emission spectrum in a green wavelength region of greater thanor equal to 500 nm and less than 550 nm, yellow light has at least onepeak of emission spectrum in a yellow wavelength region of greater thanor equal to 550 nm and less than or equal to 590 nm, and red light hasat least one peak of emission spectrum in a red wavelength region ofgreater than or equal to 600 nm and less than or equal to 740 nm.

Embodiment 1

Light-emitting elements of one embodiment of the present invention aredescribed with reference to FIGS. 1A and 1B. FIG. 1A is a schematiccross-sectional view of a light-emitting element 100 of one embodimentof the present invention, and FIG. 1B is a schematic cross-sectionalview of a light-emitting element 140 of one embodiment of the presentinvention.

In the light-emitting element 100 shown in FIG. 1A, an EL layer 130 isbetween a pair of electrodes (a first electrode 101 and a secondelectrode 102). The EL layer 130 includes a first light-emitting layer113 and a second light-emitting layer 114. In the light-emitting element100, a hole-injection layer 111, a hole-transport layer 112, anelectron-transport layer 115, and an electron-injection layer 116 areillustrated as part of the EL layer 130. However, this stacked-layerstructure is an example, and the structure of the EL layer 130 in thelight-emitting element of one embodiment of the present invention is notlimited thereto. Note that, in the light-emitting element 100, the firstelectrode 101 serves as an anode, and the second electrode 102 serves asa cathode.

The first light-emitting layer 113 includes a fluorescent material and ahost material. An emission spectrum of the first light-emitting layer113 preferably has a peak in a blue wavelength region. The secondlight-emitting layer 114 includes a phosphorescent material, a firstorganic compound, and a second organic compound. An emission spectrum ofthe second light-emitting layer 114 preferably has a peak in a yellowwavelength region. The second light-emitting layer 114 preferablyincludes one phosphorescent material. The first organic compound and thesecond organic compound form an exciplex. One of the first organiccompound and the second organic compound serves as a host material forthe second light-emitting layer 114, and the other of the first organiccompound and the second organic compound serves as an assist materialfor the second light-emitting layer 114. Note that the first organiccompound serves as the host material and the second organic compoundserves as the assist material in the following description.

When the first light-emitting layer 113 and the second light-emittinglayer 114 have the above structures, fluorescent light emission from thefirst light-emitting layer 113 (here, light emission with a peak in theblue wavelength region) and phosphorescent light emission from thesecond light-emitting layer 114 (here, light emission with a peak in theyellow wavelength region) can be efficiently obtained.

A T₁ level of the host material of the first light-emitting layer 113 ispreferably lower than T₁ levels of the first and second organiccompounds of the second light-emitting layer 114. In the firstlight-emitting layer 113, an S₁ level of the host material is preferablyhigher than an S₁ level of the fluorescent material while the T₁ levelof the host material is lower than a T₁ level of the fluorescentmaterial.

Although there is no limitation on the combination of the first organiccompound and the second organic compound in the second light-emittinglayer 114 as long as an exciplex can be formed, it is preferred that oneorganic compound be a material having a hole-transport property and theother organic compound be a material having an electron-transportproperty. In that case, a donor-acceptor excited state is formed easily,which allows an exciplex to be formed efficiently. In the case where thecombination of the first organic compound and the second organiccompound is a combination of the material having a hole-transportproperty and the material having an electron-transport property, thecarrier balance can be easily controlled depending on the mixture ratio.Specifically, the ratio of the material having a hole-transport propertyto the material having an electron-transport property is preferablywithin a range of 1:9 to 9:1 (weight ratio). Since the carrier balancecan be easily controlled in the light-emitting element 100 having thestructure, a recombination region can also be easily adjusted.

In the light-emitting element 100, a carrier recombination region ispreferably distributed to some extent. Therefore, it is preferred thatthe first light-emitting layer 113 or the second light-emitting layer114 have an appropriate degree of carrier-trapping property. It isparticularly preferred that the phosphorescent material in the secondlight-emitting layer 114 have an electron-trapping property.

Note that in the light-emitting element 100, light emitted from thefirst light-emitting layer 113 preferably has a peak on the shorterwavelength side than light emitted from the second light-emitting layer114. The luminance of a light-emitting element using the phosphorescentmaterial emitting light with a short wavelength tends to degradequickly. In view of the above, fluorescence is used for light emissionwith a short wavelength, so that a light-emitting element with lessdegradation of luminance can be provided.

Because the first light-emitting layer 113 and the second light-emittinglayer 114 are stacked to be in contact with each other in thelight-emitting element 100, the number of layers for forming the ELlayer 130 is small and productivity is high.

Further, in the light-emitting element 100, the first light-emittinglayer 113 and the second light-emitting layer 114 are made to emit lightwith different emission wavelengths, so that the light-emitting elementcan be a multicolor light-emitting element. The emission spectrum of thelight-emitting element 100 is formed by combining light having differentemission peaks, and thus has at least two peaks.

The light-emitting element 100 is suitable for obtaining white lightemission. When the first light-emitting layer 113 and the secondlight-emitting layer 114 emit light of complementary colors, white lightemission can be obtained.

In addition, white light emission with a high color rendering propertythat is formed of three primary colors or four or more colors can beobtained by using a plurality of light-emitting substances emittinglight with different wavelengths for the first light-emitting layer 113.In that case, the first light-emitting layer 113 may be divided intolayers and each of the divided layers may contain a differentlight-emitting substance from the others.

<Light Emission Mechanism of Second Light-Emitting Layer>

FIG. 2A shows a correlation of energy levels between the first organiccompound, the second organic compound, and the phosphorescent materialof the second light-emitting layer 114. The following explains whatterms and signs in FIG. 2A represent:

Host: the first organic compound;

Assist: the second organic compound;

Guest: the phosphorescent material;

S_(PH): the level of the lowest singlet excited state of the hostmaterial (the first organic compound):

T_(PH): the level of the lowest triplet excited state of the hostmaterial (the first organic compound);

T_(PG): the level of the lowest triplet excited state of the guestmaterial (the phosphorescent material);

S_(E): the level of the lowest singlet excited state of the exciplex;and

T_(E): the level of the lowest triplet excited state of the exciplex.

In the light-emitting element 100 of one embodiment of the presentinvention, the first and second organic compounds of the secondlight-emitting layer 114 form the exciplex. The level of the lowestsinglet excited state of the exciplex (S_(E)) and the level of thelowest triplet excited state of the exciplex (T_(E)) are adjacent toeach other (see Route A in FIG. 2A).

An exciplex is an excited state formed from two kinds of substances. Inthe case of photoexcitation, the exciplex is formed in such a mannerthat one molecule in an excited state takes in the other substance in aground state. The two kinds of substances that have formed the exciplexreturn to a ground state by emitting light and serve as the original twokinds of substances. In the case of electrical excitation, the exciplexcan be formed when a cationic molecule (hole) of one substance comesclose to an anionic molecule (electron) of the other substance. That is,the exciplex can be formed without formation of excitation state of anymolecule in the electrical excitation; thus, a driving voltage can belowered. Both energies of S_(E) and T_(E) of the exciplex then move tothe level of the lowest triplet excited state of the guest material (thephosphorescent material) to obtain light emission (see Route B in FIG.2A).

The above-described process of Route A and Route B is referred to asexciplex-triplet energy transfer (ExTET) in this specification and thelike. As described, in the light-emitting element of one embodiment ofthe present invention, energy can be given from the exciplex to thephosphorescent material (guest material).

When one of the first and second organic compounds receiving a hole andthe other of the first and second organic compounds receiving anelectron come close to each other, the exciplex is formed at once.Alternatively, when one substance becomes in an excited state, the oneimmediately takes in the other substance to form the exciplex.Therefore, most excitons in the second light-emitting layer 114 exist asthe exciplexes. A band gap of the exciplex is narrower than those of thefirst organic compound and the second organic compound; therefore, thedriving voltage can be lowered when the exciplex is formed byrecombination of a hole and an electron.

<Light Emission Mechanism of First Light-Emitting Layer>

In the first light-emitting layer 113, recombination of carriers formsan excited state. Note that the first light-emitting layer 113 includesthe host material and the fluorescent material. Because the amount ofthe host material is large as compared to the fluorescent material, theexcited states are formed mostly as the excited states of the hostmaterial. The ratio of singlet excited states to triplet excited statescaused by carrier recombination (hereinafter referred to as excitongeneration probability) is approximately 1:3.

First, a case where the T₁ level of the host material is higher than theT₁ level of the guest material is described below.

Energy is transferred from the host material in the triplet excitedstate to the guest material (triplet energy transfer). However, thetriplet excited state of the guest material does not offer emission oflight in a visible light region because the guest material is thefluorescent material. Thus, the triplet excited state of the hostmaterial cannot be used for light emission. Therefore, when the T₁ levelof the host material is higher than the T₁ level of the guest material,only approximately 25% of injected carriers can be used for lightemission at most.

FIG. 2B shows a correlation of energy levels between the host materialand the fluorescent material of the first light-emitting layer 113. Thefollowing explains what terms and signs in FIG. 2B represent:

Host: the host material;

Guest: the fluorescent material;

S_(FH): the level of the lowest singlet excited state of the hostmaterial;

T_(FH): the level of the lowest triplet excited state of the hostmaterial;

S_(FG): the level of the lowest singlet excited state of the guestmaterial (the fluorescent material); and

T_(FG): the level of the lowest triplet excited state of the guestmaterial (the fluorescent material).

As shown in FIG. 2B, the T₁ level of the guest material (T_(FG) in FIG.2B) is higher than the T₁ level of the guest material (T_(FH) in FIG.2B).

In addition, as shown in FIG. 2B, triplet excitons collide with eachother by triplet-triplet annihilation (TTA), and part of energy of themis converted into the level of the lowest singlet excited state of thehost material (S_(FH)). Energy is transferred from the level of thelowest singlet excited state of the host material (S_(FH)) to the levelof the lowest singlet excited state of the guest material (thefluorescent material) (S_(FG)) that is the level lower than S_(FH) (seeRoute C in FIG. 2B); and thus the fluorescent material emits light.

Because the T₁ level of the host material is lower than the T₁ level ofthe guest material, energy is transferred from T_(FG) to T_(FH) withoutdeactivation of T_(FG) (see Route D in FIG. 2B) and is utilized for TTA.

<Light Emission Mechanism of First and Second Light-Emitting Layers>

Each light emission mechanism of the first light-emitting layer 113 andthe second light-emitting layer 114 is described above. In thelight-emitting element 100 of one embodiment of the present invention,even when energy is transferred from the exciplex to the host materialof the first light-emitting layer 113 (in particular, when energy of thetriplet excited level is transferred) at an interface between the firstlight-emitting layer 113 and the second light-emitting layer 114,triplet excitation energy can be converted into light emission in thefirst light-emitting layer 113.

FIG. 3 shows a correlation of energy levels in the case where TTA isutilized in the first light-emitting layer 113 and ExTET is utilized inthe second light-emitting layer 114. The following explains what termsand signs in FIG. 3 represent:

Fluorescence EML: the fluorescent light-emitting layer (the firstlight-emitting layer 113);

Phosphorescence EML: the phosphorescent light-emitting layer (the secondlight-emitting layer 114);

T_(FH): the level of the lowest triplet excited state of the hostmaterial;

S_(FG): the level of the lowest singlet excited state of the guestmaterial (the fluorescent material);

T_(FG): the level of the lowest triplet excited state of the guestmaterial (the fluorescent material);

S_(PH): the level of the lowest singlet excited state of the hostmaterial (the first organic compound);

T_(PH): the level of the lowest triplet excited state of the hostmaterial (the first organic compound);

T_(PG): the level of the lowest triplet excited state of the guestmaterial (the phosphorescent material);

S_(E): the level of the lowest singlet excited state of the exciplex;and

T_(E): the level of the lowest triplet excited state of the exciplex.

As shown in FIG. 3, the exciplex exists only in an excited state; thus,exciton diffusion between the exciplexes is not likely to occur. Inaddition, because the excited levels of the exciplex (S_(E) and T_(E))are lower than the excited levels of the first organic compound (thehost material of the phosphorescent material) of the secondlight-emitting layer 114 (S_(PH) and T_(PH)), energy diffusion from theexciplex to the first organic compound does not occur. That is, emissionefficiency of the phosphorescent light-emitting layer (the secondlight-emitting layer 114) can be maintained because an exciton diffusiondistance of the exciplex is short in the phosphorescent light-emittinglayer (the second light-emitting layer 114). In addition, even when partof the triplet excitation energy of the exciplex of the phosphorescentlight-emitting layer (the second light-emitting layer 114) diffuses intothe fluorescent light-emitting layer (the first light-emitting layer113) through the interface between the fluorescent light-emitting layer(the first light-emitting layer 113) and the phosphorescentlight-emitting layer (the second light-emitting layer 114), energy losscan be reduced because the triplet excitation energy in the fluorescentlight-emitting layer (the first light-emitting layer 113) caused by thediffusion is used for light emission through TTA.

The light-emitting element of one embodiment of the present inventioncan have emission efficiency exceeding the exciton generationprobability when ExTET is utilized in the second light-emitting layer114 and TTA is utilized in the first light-emitting layer 113 asdescribed above. Thus, a light-emitting element with high efficiency canbe provided.

Note that in FIG. 1A, the first light-emitting layer 113 is on the sideof the first electrode 101 functioning as the anode and the secondlight-emitting layer 114 is on the side of the second electrode 102functioning as the cathode. However, the stacking order may be reversed.Specifically, as shown by the light-emitting element 140 in FIG. 1B, thefirst light-emitting layer 113 and the second light-emitting layer 114may be on the side of the electrode functioning as the cathode and onthe side of the electrode functioning as the anode, respectively. Inother words, the first light-emitting layer 113 is over the secondlight-emitting layer 114 in the light-emitting element 140.

Such a structure used for the light-emitting element 140 is preferablewhen a microcavity structure (described later) is employed because theoptical path length of the second light-emitting layer 114 and/or thefirst light-emitting layer 113 is easily adjusted.

The details of the components of the light-emitting element 100 of oneembodiment of the present invention are described below.

<Electrode>

The first electrode 101 and the second electrode 102 have functions ofinjecting holes and electrons, respectively, into the firstlight-emitting layer 113 and the second light-emitting layer 114. Theseelectrodes can be formed of a metal, an alloy, or a conductive compound,or a mixture or a stack thereof, for example. A typical example of themetal is aluminum, besides, a transition metal such as silver, tungsten,chromium, molybdenum, copper, or titanium, an alkali metal such aslithium or cesium, or a Group 2 metal such as calcium or magnesium canbe used. As the transition metal, a rare earth metal may be used. Analloy containing any of the above metals can be used as the alloy, andMgAg and AlLi can be given as examples. As the conductive compound, ametal oxide such as indium oxide-tin oxide (indium tin oxide) can begiven. It is also possible to use an inorganic carbon-based materialsuch as graphene as the conductive compound. As described above, thefirst electrode 101 and/or the second electrode 102 may be formed bystacking two or more of these materials.

Light emitted from the first light-emitting layer 113 and the secondlight-emitting layer 114 is extracted through the first electrode 101and/or the second electrode 102. Therefore, at least one of theelectrodes transmits visible light. In the case where the electrodethrough which light is extracted is formed using a material with lowlight permeability, such as metal or alloy, the first electrode 101, thesecond electrode 102, or part thereof is formed to a thickness that isthin enough to transmit visible light. In this case, the specificthickness is in a range from 1 nm to 10 nm.

<First Light-Emitting Layer>

The first light-emitting layer 113 includes the host material and thefluorescent material. In the first light-emitting layer 113, the hostmaterial is present in the highest proportion by weight, and thefluorescent material is dispersed in the host material. The S₁ level ofthe host material is higher than the S₁ level of the fluorescentmaterial, and the T₁ level of the host material is lower than the T₁level of the fluorescent material.

An anthracene derivative or a tetracene derivative is preferably used asthe host material. This is because these derivatives each have a high S₁level and a low T₁ level. Specific examples include9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (PCzPA),3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (PCPN),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (CzPA),7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(2mBnfPPA), and9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene(FLPPA). Besides, 5,12-diphenyltetracene,5,12-bis(biphenyl-2-yl)tetracene, and the like can be given.

Examples of the fluorescent material include a pyrene derivative, ananthracene derivative, a triphenylene derivative, a fluorene derivative,a carbazole derivative, a dibenzothiophene derivative, a dibenzofuranderivative, a dibenzoquinoxaline derivative, a quinoxaline derivative, apyridine derivative, a pyrimidine derivative, a phenanthrene derivative,and a naphthalene derivative. A pyrene derivative is particularlypreferable because it has a high emission quantum yield. Specificexamples of the pyrene derivative includeN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(1,6mMemFLPAPrn),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenylpyrene-1,6-diamine(1,6FLPAPrn),N,N′-bis(dibenzofuran-2-yl)-N,N′-diphenylpyrene-1,6-diamine (1,6FrAPrn),and N,N′-bis(dibenzothiophen-2-yl)-N,N′-diphenylpyrene-1,6-diamine(1,6ThAPrn).

<Second Light-Emitting Layer>

The second light-emitting layer 114 includes the first organic compound,the second organic compound, and the phosphorescent material. Note thatthe first organic compound serves as the host material and the secondorganic compound serves as the assist material in the followingdescription.

In the second light-emitting layer 114, the host material (the firstorganic compound) is present in the highest proportion by weight, andthe phosphorescent material is dispersed in the host material. The T₁level of the host material (the first organic compound) of the secondlight-emitting layer 114 is preferably higher than the T₁ level of thefluorescent material of the first light-emitting layer 113.

As the phosphorescent material, an iridium-, rhodium-, or platinum-basedorganometallic complex or metal complex can be used; in particular, anorganoiridium complex such as an iridium-based ortho-metalated complexis preferable. As an ortho-metalated ligand, a 4H-triazole ligand, a1H-triazole ligand, an imidazole ligand, a pyridine ligand, a pyrimidineligand, a pyrazine ligand, an isoquinoline ligand, or the like can begiven. As the metal complex, a platinum complex having a porphyrinligand or the like can be given.

As the phosphorescent material, a material with a spectrum peak in theyellow wavelength region is preferred. In addition, it is preferred thatan emission spectrum of the material with the peak in the yellowwavelength region include spectral components in the green and redwavelength regions.

Examples of the host material (the first organic compound) include azinc- or aluminum-based metal complex, an oxadiazole derivative, atriazole derivative, a benzimidazole derivative, a quinoxalinederivative, a dibenzoquinoxaline derivative, a dibenzothiophenederivative, a dibenzofuran derivative, a pyrimidine derivative, atriazine derivative, a pyridine derivative, a bipyridine derivative, anda phenanthroline derivative. Other examples are an aromatic amine and acarbazole derivative.

As the second organic compound (the assist material), a substance whichcan form an exciplex together with the first organic compound is used.In this case, it is preferable that the first organic compound, thesecond organic compound, and the phosphorescent material be selectedsuch that the emission peak of the exciplex overlaps with an adsorptionband, specifically an adsorption band on the longest wavelength side, ofa triplet metal to ligand charge transfer (MLCT) transition of thephosphorescent material. This makes it possible to provide alight-emitting element with drastically improved emission efficiency.However, if a material exhibiting thermally activated delayedfluorescence (TADF) is used instead of the phosphorescent material, itis preferred that an adsorption band on the longest wavelength side bean absorption band of a singlet. The TADF material is explained later.

There is no limitation on the emission colors of the firstlight-emitting material and the second light-emitting material, and theymay be the same or different. Light emitted from the light-emittingmaterials is mixed and extracted out of the element; therefore, forexample, in the case where their emission colors are complementarycolors, the light-emitting element can emit white light. Inconsideration of the reliability of the light-emitting element, theemission peak wavelength of the first light-emitting material ispreferably shorter than that of the second light-emitting material. Forexample, it is preferable that the first light-emitting material emitblue light and the second light-emitting material emit yellow light.

<Other Layers>

As illustrated in FIG. 1A, the light-emitting element 100 of oneembodiment of the present invention may include another layer besidesthe first light-emitting layer 113 and the second light-emitting layer114. For example, the light-emitting element may include ahole-injection layer, a hole-transport layer, an electron-blockinglayer, a hole-blocking layer, an electron-transport layer, anelectron-injection layer, and the like. Furthermore, each of theselayers may be formed of a plurality of layers. These layers can reduce acarrier injection barrier, improve a carrier transport property, orsuppress a quenching phenomenon by an electrode, thereby contributing toan improvement in emission efficiency or a reduction in a drivingvoltage. Each of these layers can be formed by any one or anycombination of the following methods: an evaporation method (including avacuum evaporation method), a printing method (such as relief printing,intaglio printing, gravure printing, planography printing, and stencilprinting), an ink-jet method, a coating method, and the like.

<Hole-Injection Layer>

The hole-injection layer 111 has a function of reducing a barrier forhole injection from the first electrode 101 to promote hole injectionand is formed using a transition metal oxide, a phthalocyaninederivative, or an aromatic amine, for example. As the transition metaloxide, molybdenum oxide, vanadium oxide, ruthenium oxide, tungstenoxide, manganese oxide, or the like can be given. As the phthalocyaninederivative, phthalocyanine, metal phthalocyanine, or the like can begiven. As the aromatic amine, a benzidine derivative, a phenylenediaminederivative, or the like can be given. It is also possible to use a highmolecular compound such as polythiophene or polyaniline; a typicalexample thereof is poly(ethylenedioxythiophene)/poly(styrenesulfonicacid), which is self-doped polythiophene.

As the hole-injection layer 111, a composite material of ahole-transport material and a material having a property of acceptingelectrons from the hole-transport material can also be used.Alternatively, a stack of a layer containing a material having anelectron accepting property and a layer containing a hole-transportmaterial may also be used. In a steady state or in the presence of anelectric field, electric charge can be transferred between thesematerials. As examples of the material having an electron acceptingproperty, organic acceptors such as a quinodimethane derivative, achloranil derivative, and a hexaazatriphenylene derivative can be given.Alternatively, a transition metal oxide such as an oxide of a metal fromGroup 4 to Group 8 can also be used. Specifically, vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, rhenium oxide, or the like can be used.In particular, molybdenum oxide is preferable because it is stable inthe air, has a low hygroscopic property, and is easily handled.

A material having a property of transporting more holes than electronscan be used as the hole-transport material, and a material having a holemobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Specifically, anaromatic amine, a carbazole derivative, an aromatic hydrocarbon, astilbene derivative, or the like can be used. Furthermore, thehole-transport material may be a high molecular compound.

<Hole-Transport Layer>

The hole-transport layer 112 is a layer containing a hole-transportmaterial and can be formed using any of the materials given as examplesof the material of the hole-injection layer 111. In order that thehole-transport layer 112 has a function of transporting holes injectedinto the hole-injection layer 111 to the first light-emitting layer 113,the highest occupied molecular orbital (HOMO) level of thehole-transport layer 112 is preferably equal or close to the HOMO levelof the hole-injection layer 111.

<Electron-Transport Layer>

The electron-transport layer 115 has a function of transporting, to thesecond light-emitting layer 114, electrons injected from the secondelectrode 102 through the electron-injection layer 116. A materialhaving a property of transporting more electrons than holes can be usedas an electron-transport material, and a material having an electronmobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Specific examplesinclude a metal complex having a quinoline ligand, a benzoquinolineligand, an oxazole ligand, or a thiazole ligand; an oxadiazolederivative; a triazole derivative; a phenanthroline derivative; apyridine derivative; and a bipyridine derivative.

<Electron-Injection Layer>

The electron-injection layer 116 has a function of reducing a barrierfor electron injection from the second electrode 102 to promote electroninjection and can be formed using a Group 1 metal or a Group 2 metal, oran oxide, a halide, or a carbonate of any of the metals, for example.Alternatively, a composite material containing an electron-transportmaterial (described above) and a material having a property of donatingelectrons to the electron-transport material can also be used. As thematerial having an electron donating property, a Group 1 metal, a Group2 metal, an oxide of any of the metals, or the like can be given.

<Substrate, FET, and the Like>

The light-emitting element 100 is fabricated over a substrate of glass,plastic, or the like. As the way of stacking layers over the substrate,layers may be sequentially stacked from the first electrode 101 side orsequentially stacked from the second electrode 102 side. Thelight-emitting element may be formed over an electrode electricallyconnected to a field-effect transistor (FET), for example, that isformed over a substrate of glass, plastic, or the like. Accordingly, anactive matrix light-emitting device in which the FET controls the driveof the light-emitting element can be fabricated.

Although the light-emitting material included in the secondlight-emitting layer 114 is the phosphorescent material in the abovedescription, the light-emitting material is not limited thereto. As thelight-emitting material included in the second light-emitting layer 114,any material can be used as long as the material can convert the tripletexcitation energy into light emission. As an example of the materialthat can convert the triplet excitation energy into light emission, aTADF material is given in addition to a phosphorescent material.Therefore, it is acceptable that the “phosphorescent material” in thedescription is replaced with the “TADF material. Note that the TADFmaterial is a substance that can up-convert a triplet excited state intoa singlet excited state (i.e., reverse intersystem crossing is possible)using a little thermal energy and efficiently exhibits light emission(fluorescence) from the singlet excited state. The TADF is efficientlyobtained under the condition where the difference in energy between thetriplet excited level and the singlet excited level is greater than orequal to 0 eV and less than or equal to 0.2 eV, preferably greater thanor equal to 0 eV and less than or equal to 0.1 eV.

It is to be noted that this embodiment can be combined appropriatelywith other embodiments.

Embodiment 2

Light-emitting elements with different structures from those of thelight-emitting elements 100 and 140 shown in Embodiment 1 are describedin this embodiment with reference to FIGS. 4A and 4B. FIG. 4A is aschematic cross-sectional view of a light-emitting element 150 of oneembodiment of the present invention, and FIG. 4B is a schematiccross-sectional view of a light-emitting element 160 of one embodimentof the present invention.

The light-emitting element 150 is different from the light-emittingelement 100 in that a separation layer 120 is provided between the firstlight-emitting layer 113 and the second light-emitting layer 114. Theseparation layer 120 is in contact with the first light-emitting layer113 and the second light-emitting layer 114. The structures of the otherlayers are similar to those in Embodiment 1; therefore, descriptionthereof is omitted.

The separation layer 120 is provided to prevent energy transfer by theDexter mechanism (particularly triplet energy transfer) from the firstorganic compound in an excited state or the phosphorescent material inan excited state which is generated in the second light-emitting layer114 to the host material or the fluorescent material in the firstlight-emitting layer 113. Therefore, the thickness of the separationlayer may be approximately several nanometers, specifically 0.1 nm ormore and 20 nm or less, 1 nm or more and 10 nm or less, or 1 nm or moreand 5 nm or less.

The separation layer 120 may contain a single material or both ahole-transport material and an electron-transport material. In the caseof a single material, a bipolar material may be used. The bipolarmaterial here refers to a material in which the ratio between theelectron mobility and the hole mobility is 100 or less. As a materialcontained in the separation layer 120, the hole-transport material, theelectron-transport material, or the like given as an example inEmbodiment 1 can be used. Furthermore, at least one of materialscontained in the separation layer 120 may be the same as the hostmaterial (the first organic compound) of the second light-emitting layer114. This facilitates the manufacture of the light-emitting element andreduces the driving voltage.

For example, when the separation layer 120 is formed of the samematerials as the host material (the first organic compound) and theassist material (the second organic compound) of the secondlight-emitting layer 114, the first light-emitting layer 113 and thesecond light-emitting layer 114 are stacked with each other while thelayer (the separation layer 120) not including the phosphorescentmaterial of the second light-emitting layer 114 is providedtherebetween. In the case of such a structure, depending on using or notusing the phosphorescent material, the second light-emitting layer 114or the separation layer 120 can be deposited. In other words, theseparation layer 120 includes a region not including the phosphorescentmaterial while the second light-emitting layer 114 includes a regionincluding the phosphorescent material. In the case of such a structure,the separation layer 120 and the second light-emitting layer 114 can beformed in the same chamber. Thus, the manufacturing cost can be reduced.

Alternatively, at least one of materials contained in the separationlayer 120 may have a higher T₁ level than the host material (the firstorganic compound) of the second light-emitting layer 114.

The recombination region can be adjusted by adjusting the mixture ratioof the hole-transport material and the electron-transport material,whereby the emission color can be controlled. For example, in the casewhere the first electrode 101 and the second electrode 102 serve as ananode and a cathode, respectively, the recombination region can beshifted from the first electrode 101 side to the second electrode 102side by increasing the proportion of the hole-transport material in theseparation layer 120. As a result, the contribution of the secondlight-emitting layer 114 to light emission can be increased. Incontrast, by increasing the proportion of the electron-transportmaterial, the recombination region can be shifted from the secondelectrode 102 side to the first electrode 101 side, so that thecontribution of the first light-emitting layer 113 to light emission canbe increased. In the case where the first light-emitting layer 113 andthe second light-emitting layer 114 have different emission colors, theemission color of the light-emitting element can be changed as a whole.

The hole-transport material and the electron-transport material may forman exciplex in the separation layer 120, which effectively preventsexciton diffusion. Specifically, energy transfer from the host material(the first organic compound) of the second light-emitting layer 114 inan excited state or the phosphorescent material in an excited state tothe host material of the first light-emitting layer 113 or thefluorescent material can be prevented.

As in the light-emitting element 140 described in Embodiment 1, thefirst light-emitting layer 113 may be positioned over the secondlight-emitting layer 114. Specifically, as shown by the light-emittingelement 160 in FIG. 4B, it is acceptable that the second light-emittinglayer 114 is provided over the hole-transport layer 112, and the firstlight-emitting layer 113 is provided over the second light-emittinglayer 114 with the separation layer 120 provided therebetween.

The structure described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, a light-emitting element of one embodiment of thepresent invention is described with reference to FIG. 5. FIG. 5 is aschematic cross-sectional view of a light-emitting element 170 of oneembodiment of the present invention.

The light-emitting element 170 includes a plurality of light-emittingunits (a first light-emitting unit 131 and a second light-emitting unit132 in FIG. 5) between the first electrode 101 and the second electrode102. One light-emitting unit has the same structure as the EL layer 130illustrated in FIG. 1A or 1B. That is, the light-emitting element 100 inFIG. 1A includes one light-emitting unit while the light-emittingelement 170 includes the plurality of light-emitting units.

In the light-emitting element 170 shown in FIG. 5, the firstlight-emitting unit 131 and the second light-emitting unit 132 arestacked, and a charge generation layer 133 is provided between the firstlight-emitting unit 131 and the second light-emitting unit 132. Notethat the first light-emitting unit 131 and the second light-emittingunit 132 may have the same structure or different structures.

The charge generation layer 133 may include a composite material of anorganic compound and metal oxide. For the composite material, thecomposite material that can be used for the hole-injection layer 111described above may be used. As the organic compound, a variety ofcompounds such as an aromatic amine compound, a carbazole compound, anaromatic hydrocarbon, and a high molecular compound (such as anoligomer, a dendrimer, or a polymer) can be used. An organic compoundhaving a hole mobility of 1×10⁻⁶ cm²/Vs or higher is preferably used.Note that any other substance may be used as long as the substance has ahole-transport property higher than an electron-transport property.Since the composite material of an organic compound and a metal oxide issuperior in carrier-injecting property and carrier-transportingproperty, low-voltage driving or low-current driving can be realized.Note that when a surface of a light-emitting unit on the anode side isin contact with the charge generation layer 133, the charge generationlayer 133 can also serve as a hole-transport layer of the light-emittingunit; thus, a hole-transport layer does not need to be formed in thelight-emitting unit.

The charge generation layer 133 may have a stacked-layer structure of alayer containing the composite material of an organic compound and ametal oxide and a layer containing another material. For example, thecharge generation layer 133 may be formed using a combination of a layercontaining the composite material of an organic compound and a metaloxide with a layer containing one compound selected from amongelectron-donating substances and a compound having a highelectron-transporting property. Further, the charge generation layer 133may be formed using a combination of a layer containing the compositematerial of an organic compound and a metal oxide with a transparentconductive film.

In any case, as the charge-generation layer 133, which is providedbetween the first light-emitting unit 131 and the second light-emittingunit 132, acceptable is a layer which injects electrons into thelight-emitting unit on one side and injects holes into thelight-emitting unit on the other side when voltage is applied to thefirst electrode 101 and the second electrode 102. For example, in FIG.5, when a voltage is applied such that a potential of the firstelectrode 101 is higher than a potential of the second electrode 102,any structure may be used for the charge generation layer 133, as longas the charge generation layer 133 injects electrons and holes into thefirst light-emitting unit 131 and the second light-emitting unit 132,respectively.

In FIG. 5, the light-emitting element having two light-emitting units isdescribed; however, one embodiment of the present invention can besimilarly applied to a light-emitting element in which three or morelight-emitting units are stacked. With a plurality of light-emittingunits partitioned by the charge generation layer between a pair ofelectrodes as in the light-emitting element 170, it is possible toprovide a light-emitting element which can emit light with highluminance with the current density kept low and has a long lifetime. Alight-emitting device that can be driven at a low voltage and has lowpower consumption can be realized.

When the above-described structure of the EL layer 130 is used for atleast one of the plurality of units, the number of manufacturing stepsof the unit can be reduced; thus, a multicolor light-emitting elementwhich is advantageous for practical application can be provided.

The above-described structure can be combined with any of the structuresin this embodiment and the other embodiments.

Embodiment 4

In this embodiment, a light-emitting device manufactured using thelight-emitting element described in any of Embodiments 1 to 3 will bedescribed with reference to FIGS. 6A and 6B.

FIG. 6A is a top view illustrating a light-emitting device 600 and FIG.6B is a cross-sectional view taken along the dashed-dotted line A-B andthe dashed-dotted line C-D in FIG. 6A. The light-emitting device 600includes driver circuit portions (a source line driver circuit portion601 and a gate line driver circuit portion 603) and a pixel portion 602.Note that the source line driver circuit portion 601, the gate linedriver circuit portion 603, and the pixel portion 602 have a function ofcontrolling light emission of a light-emitting element.

The light-emitting device 600 also includes an element substrate 610, asealing substrate 604, a sealing member 605, a region 607 surrounded bythe sealing member 605, a lead wiring 608, and an FPC 609.

Note that the lead wiring 608 is a wiring for transmitting signals to beinput to the source line driver circuit portion 601 and the gate linedriver circuit portion 603 and for receiving a video signal, a clocksignal, a start signal, a reset signal, and the like from the FPC 609serving as an external input terminal. Although only the FPC 609 isshown here, the FPC 609 may be provided with a printed wiring board(PWB).

In the source line driver circuit portion 601, a CMOS circuit is formedin which an n-channel FET 623 and a p-channel FET 624 are combined. Notethat the source line driver circuit portion 601 or the gate line drivercircuit portion 603 may be formed with various kinds of CMOS circuits,NMOS circuits, and PMOS circuits. In this embodiment, although adriver-integrated type structure in which a driver circuit portion isformed over a substrate is described, a driver circuit portion is notnecessarily formed over a substrate but can be formed outside asubstrate.

The pixel portion 602 includes a switching FET 611, a current controlFET 612, and a first electrode 613 electrically connected to a drain ofthe current control FET 612. It is to be noted that an insulator 614 isformed to cover an edge of the first electrode 613. As the insulator614, for example, a positive type photosensitive acrylic resin film canbe used.

The insulator 614 is formed to have a curved surface with curvature atan upper edge or a lower edge thereof in order to obtain favorablecoverage. For example, in the case where positive photosensitive acrylicis used for a material of the insulator 614, it is preferred that onlythe upper end portion of the insulator 614 has a curved surface with acurvature radius (0.2 μm to 3 μm). As the insulator 614, either anegative photosensitive resin or a positive photosensitive resin can beused.

Note that there is no particular limitation on a structure of each ofthe FETs (the FETs 611, 612, 623, and 624). For example, a staggeredtransistor can be used. In addition, there is no particular limitationon a conductivity type of each transistor. For these transistors, n-typeand p-type transistors may be used, or either n-type transistors orp-type transistors may be used, for example. Furthermore, there is noparticular limitation on crystallinity of a semiconductor film used forthe transistor. For example, an amorphous semiconductor film or acrystalline semiconductor film may be used. Examples of a semiconductormaterial include Group 13 semiconductors (e.g., gallium), Group 14semiconductors (e.g., silicon), compound semiconductors (including oxidesemiconductors), organic semiconductors, and the like. For example, anoxide semiconductor that has an energy gap of 2 eV or more, preferably2.5 eV or more, further preferably 3 eV or more is preferably used forthe transistors, so that the off-state current of the transistors can bereduced. Examples of the oxide semiconductor include an In—Ga oxide, anIn—M—Zn oxide (M is Al, Ga, Y, Zr, La, Ce, or Nd), and the like.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. Here, the first electrode 613 serves as an anode and thesecond electrode 617 serves as a cathode.

The EL layer 616 can be formed by a method such as an evaporation method(including a vacuum evaporation method), a printing method (such asrelief printing, intaglio printing, gravure printing, planographyprinting, and stencil printing), an ink-jet method, or a coating method.The EL layer 616 has the structure described in any of Embodiments 1 to3. As another material included in the EL layer 616, a low molecularcompound or a high molecular compound (including an oligomer or adendrimer) may be used.

Note that the light-emitting element 618 is formed with the firstelectrode 613, the EL layer 616, and the second electrode 617. Thelight-emitting element 618 has any of the structures shown inEmbodiments 1 to 3. In the case where the pixel portion includes aplurality of light-emitting elements, the pixel portion may include boththe light-emitting element described in any of Embodiments 1 to 3 and alight-emitting element having a different structure.

When the sealing substrate 604 and the element substrate 610 areattached to each other with the sealing member 605, the light-emittingelement 618 is provided in the region 607 surrounded by the elementsubstrate 610, the sealing substrate 604, and the sealing member 605.Note that the region 607 is filled with filler, specifically filled withan inert gas (such as nitrogen or argon) in some cases, or filled withthe sealing member 605 in other cases. It is preferable that the sealingsubstrate be provided with a recessed portion and the drying agent (notillustrated in the drawing) be provided in the recessed portion, inwhich case deterioration due to influence of moisture can be suppressed.

An epoxy-based resin or glass frit is preferably used for the sealingmember 605. The material preferably allows as little moisture and oxygenas possible to penetrate. As the sealing substrate 604, a glasssubstrate, a quartz substrate, or a plastic substrate formed of fiberreinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester,acrylic, or the like can be used.

As described above, the light-emitting device which uses thelight-emitting element described in any of Embodiments 1 to 3 can beobtained.

The light-emitting device 600 in this embodiment is fabricated using thelight-emitting element described in any of Embodiments 1 to 3 and thuscan have favorable characteristics. Specifically, since thelight-emitting element described in any of Embodiments 1 to 3 has highemission efficiency, the light-emitting device can have reduced powerconsumption. In addition, since the light-emitting element is easy tomass-produce, the light-emitting device can be provided at low cost.

FIGS. 7A and 7B each illustrate an example of a cross-sectional view ofa light-emitting device in which full color display is achieved byformation of a light-emitting element exhibiting white light emissionand use of coloring layers (color filters) and the like.

In FIG. 7A, a substrate 1001, a base insulating film 1002, a gateinsulating film 1003, gate electrodes 1006, 1007, and 1008, a firstinterlayer insulating film 1020, a second interlayer insulating film1021, a peripheral portion 1042, a pixel portion 1040, a driver circuitportion 1041, first electrodes 1024Y, 1024R, 1024G, and 1024B oflight-emitting elements, a partition 1025, an EL layer 1028, a secondelectrode 1026 of the light-emitting elements, a sealing substrate 1031,a sealing member 1032, and the like are illustrated.

In FIG. 7A, coloring layers (a red coloring layer 1034R, a greencoloring layer 1034G, a blue coloring layer 1034B, and a yellow coloringlayer 1034Y) are provided on a transparent base material 1033. Further,a black layer (black matrix) 1035 may be provided. The transparent basematerial 1033 provided with the coloring layers and the black layer ispositioned and fixed to the substrate 1001. Note that the coloringlayers and the black layer are covered with an overcoat layer 1036. Inthe structure in FIG. 7A, red light, blue light, green light, and yellowlight transmit the coloring layers, and thus an image can be displayedwith the use of pixels of four colors.

FIG. 7B illustrates an example in which coloring layers (the redcoloring layer 1034R, the green coloring layer 1034G, and the bluecoloring layer 1034B) are formed between the gate insulating film 1003and the first interlayer insulating film 1020. As in the structure, thecoloring layers may be provided between the substrate 1001 and thesealing substrate 1031. Note that the yellow coloring layer is notnecessarily provided as shown in FIG. 7B because the light-emittingelement of one embodiment of the present invention can emit light with ayellow wavelength.

The above-described light-emitting device is a light-emitting devicehaving a structure in which light is extracted from the substrate 1001side where the FETs are formed (a bottom emission structure), but alight-emitting device having a structure in which light is extractedfrom the sealing substrate 1031 side (a top emission structure) is alsoacceptable.

FIG. 8 is a cross-sectional view of a light-emitting device having a topemission structure. In this case, as the substrate 1001, a substratethat does not transmit light can be used. The process up to the step offorming a connection electrode which connects the FET and the anode ofthe light-emitting element is performed in a manner similar to that ofthe light-emitting device having a bottom emission structure. Then, athird interlayer insulating film 1037 is formed to cover an electrode1022. This insulating film may function for planarization. The thirdinterlayer insulating film 1037 can be formed by using a materialsimilar to that of the second interlayer insulating film, or can beformed by using any other materials.

The first electrodes 1024Y, 1024R, 1024E and 1024B of the light-emittingelements each serve as an anode here, but may serve as a cathode.Further, in the case of a light-emitting device having a top emissionstructure as illustrated in FIG. 8, the first electrodes 1024Y, 1024R,1024G, and 1024B are preferably reflective electrodes. The EL layer 1028is formed to have a structure similar to the structure of the EL layer130, which is described in any of Embodiments 1 to 3, with which whitelight emission can be obtained.

In FIG. 8, a second electrode 1026 is formed over the EL layer 1028. Thesecond electrode 1026 may be a semi-transmissive and semi-reflectiveelectrode, and a micro optical resonator (microcavity) structureutilizing a resonant effect of light between the second electrode 1026and the first electrodes 1024Y, 1024R, 1024G, and 1024B may be used soas to increase the intensity of light having a specific wavelength.

In the case of a top emission structure as illustrated in FIG. 8,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G the blue coloring layer 1034B, and the yellow coloring layer1034Y) are provided. The sealing substrate 1031 may be provided with ablack layer 1035 which is positioned between pixels. The color layers(the red coloring layer 1034R, the green coloring layer 1034G, and theblue coloring layer 1034B, and the yellow coloring layer 1034Y) and theblack layer 1035 may be covered with the overcoat layer (not illustratedin the drawing). Note that a light-transmitting substrate is used as thesealing substrate 1031.

FIG. 8 shows the structure provided with the light-emitting elementsfrom which white light emission can be obtained and the coloring layersfor the light-emitting elements as an example; however, the structure isnot limited thereto. For example, as shown in FIG. 9A, a structureincluding the light-emitting elements from which white light emissioncan be obtained, the red coloring layer 1034R, the green coloring layer1034G, and the yellow coloring layer 1034Y while not including the bluecoloring layer may be employed in order to achieve full color displaywith the four colors of red, green, blue, and yellow. Alternatively, asshown in FIG. 9B, a structure including the light-emitting elements fromwhich white light emission can be obtained, the red coloring layer1034R, and the green coloring layer 1034G while not including the bluecoloring layer and the yellow coloring layer may be employed in order toachieve full color display with the four colors of red, green, blue, andyellow. The structure as shown in FIG. 8 where the coloring layer isprovided to each of the light-emitting element from which white lightemission can be obtained is effective to suppress reflection of outsidelight. In contrast, the structure as shown in FIG. 9B where thelight-emitting elements from which white light emission can be obtainedare provided with the red coloring layer and the green coloring layerand without the blue and yellow coloring layers is effective to reducepower consumption because of small energy loss of light emitted from thelight-emitting elements.

Alternatively, a structure as shown in FIG. 10A, including thelight-emitting elements from which white light emission can be obtainedand the coloring layers for the light-emitting layers to achieve fullcolor display with three colors of red, green, and blue, may beemployed. Alternatively, a structure as shown in FIG. 10B, including thelight-emitting elements from which white light emission can be obtained,the red coloring layer 1034R, and the green coloring layer 1034G whilenot including the blue coloring layer to achieve full color display withthree colors of red, green, and blue, may be employed.

Note that FIGS. 9A and 9B and FIGS. 10A and 10B are each a schematiccross-sectional view for illustrating the light-emitting device of oneembodiment of the present invention, and the driver circuit portion1041, the peripheral portion 1042, and the like, which are shown in FIG.8, are not illustrated therein. In the structures of FIGS. 9A and 9B andFIGS. 10A and 10B, the microcavity structure may be employed as in thestructure of FIG. 8.

The light-emitting device in this embodiment is fabricated using thelight-emitting element described in any of Embodiments 1 to 3 and thuscan have favorable characteristics. Specifically, since thelight-emitting element described in any of Embodiments 1 to 3 has highemission efficiency, the light-emitting device can have reduced powerconsumption. When the light-emitting element described in any ofEmbodiments 1 to 3 is combined with the coloring layer such as the colorfilter, an optimum element structure can be formed from which whitelight emission can be obtained. In addition, since the structure of thelight-emitting element described in any of Embodiments 1 to 3 is easy tomass-produce, the light-emitting device can be provided at low cost.

The above-described structure can be combined with any of the structuresin this embodiment and the other embodiments.

Embodiment 5

In this embodiment, a display device that includes a lithe-emittingdevice of one embodiment of the present invention is described withreference to FIGS. 11A and 11B.

FIG. 11A is a block diagram illustrating the display device of oneembodiment of the present invention, and FIG. 11B is a circuit diagramillustrating a pixel circuit of the display device of one embodiment ofthe present invention.

The display device illustrated in FIG. 11A includes a region includingpixels of display elements (hereinafter the region is referred to as apixel portion 802), a circuit portion provided outside the pixel portion802 and including a circuit for driving the pixels (hereinafter theportion is referred to as a driver circuit portion 804), circuits havinga function of protecting elements (hereinafter the circuits are referredto as protection circuits 806), and a terminal portion 807. Note thatthe protection circuits 806 are not necessarily provided.

A part or the whole of the driver circuit portion 804 is preferablyformed over a substrate over which the pixel portion 802 is formed.Thus, the number of components and the number of terminals can bereduced. When a part or the whole of the driver circuit portion 804 isnot formed over the substrate over which the pixel portion 802 isformed, the part or the whole of the driver circuit portion 804 can bemounted by COG or tape automated bonding (TAB).

The pixel portion 802 includes circuits for driving a plurality ofdisplay elements arranged in X rows (X is a natural number of 2 or more)and Y columns (Y is a natural number of 2 or more) (hereinafter, suchcircuits are referred to as pixel circuits 801). The driver circuitportion 804 includes driver circuits such as a circuit for supplying asignal (scan signal) to select a pixel (hereinafter the circuit isreferred to as a gate driver 804 a) and a circuit for supplying a signal(data signal) to drive a display element in a pixel (hereinafter, thecircuit is referred to as a source driver 804 b).

The gate driver 804 a includes a shift register or the like. The gatedriver 804 a receives a signal for driving the shift register throughthe terminal portion 807 and outputs a signal. For example, the gatedriver 804 a receives a start pulse signal, a clock signal, or the likeand outputs a pulse signal. The gate driver 804 a has a function ofcontrolling the potentials of wirings supplied with scan signals(hereinafter, such wirings are referred to as scan lines GL_1 to GL_X).Note that a plurality of gate drivers 804 a may be provided to controlthe scan lines GL_1 to GL_X separately. Alternatively, the gate driver804 a has a function of supplying an initialization signal. Not limitedthereto, the gate driver 804 a can supply another signal.

The source driver 804 b includes a shift register or the like. Thesource driver 804 b receives a signal (video signal) from which a datasignal is derived, as well as a signal for driving the shift register,through the terminal portion 807. The source driver 804 b has a functionof generating a data signal to be written in the pixel circuits 801based on the video signal. In addition, the source driver 804 b has afunction of controlling output of a data signal in response to a pulsesignal produced by input of a start pulse signal, a clock signal, or thelike. Further, the source driver 804 b has a function of controlling thepotentials of wirings supplied with data signals (hereinafter, suchwirings are referred to as data lines DL_1 to DL_Y). Alternatively, thesource driver 804 b has a function of supplying an initializationsignal. Not limited thereto, the source driver 804 b can supply anothersignal.

Alternatively, the source driver 804 b is formed using a plurality ofanalog switches or the like, for example. The source driver 804 b canoutput, as the data signals, signals obtained by time-dividing the videosignal by sequentially turning on the plurality of analog switches. Thesource driver 804 b may include a shift register or the like.

A pulse signal and a data signal are input, through one of the pluralityof scan lines GL supplied with scan signals and one of the plurality ofdata lines DL supplied with data signals, respectively, to each of theplurality of the pixel circuits 801. Writing and holding of the datasignal in each of the plurality of pixel circuits 801 are controlled bythe gate driver 804 a. For example, to the pixel circuit 801 in the m-throw and the n-th column (m is a natural number of less than or equal toX, and n is a natural number of less than or equal to Y), a pulse signalis input from the gate driver 804 a through the scan line GL_m, and adata signal is input from the source driver 804 b through the data lineDL_n in accordance with the potential of the scan line GL_m.

The protection circuit 806 shown in FIG. 11A is connected to, forexample, the scan line GL between the gate driver 804 a and the pixelcircuits 801. Alternatively, the protection circuit 806 is connected tothe data line DL between the source driver 804 b and the pixel circuit801. Alternatively, the protection circuit 806 can be connected to awiring between the gate driver 804 a and the terminal portion 807.Alternatively, the protection circuit 806 can be electrically connectedto a wiring between the source driver 804 b and the terminal portion807. Note that the terminal portion 807 means a portion having terminalsfor inputting power, control signals, and video signals to the displaydevice from external circuits.

The protection circuit 806 is a circuit which electrically conducts awiring connected to the protection circuit to another wiring when apotential out of a certain range is supplied to the wiring connected tothe protection circuit.

As illustrated in FIG. 11A, the protection circuits 806 are provided forthe pixel portion 802 and the driver circuit portion 804, so that theresistance of the display device to overcurrent generated byelectrostatic discharge (ESD) or the like can be improved. Note that theconfiguration of the protection circuits 806 is not limited to that, andfor example, the protection circuit 806 may be configured to beconnected to the gate driver 804 a or the protection circuit 806 may beconfigured to be connected to the source driver 804 b. Alternatively,the protection circuit 806 may be configured to be connected to theterminal portion 807.

In FIG. 11A, an example in which the driver circuit portion 804 includesthe gate driver 804 a and the source driver 804 b is shown; however, thestructure is not limited thereto. For example, only the gate driver 804a may be formed and a separately prepared substrate where a sourcedriver circuit is formed (e.g., a driver circuit substrate formed with asingle crystal semiconductor film or a polycrystalline semiconductorfilm) may be mounted.

Each of the plurality of pixel circuits 801 in FIG. 11A can have thestructure illustrated in FIG. 11B, for example.

The pixel circuit 801 shown in FIG. 11B includes transistors 852 and854, a capacitor 862, and a light-emitting element 872.

One of a source electrode and a drain electrode of the transistor 852 iselectrically connected to a wiring to which a data signal is supplied(hereinafter referred to as a signal line DL_n). A gate electrode of thetransistor 852 is electrically connected to a wiring to which a gatesignal is supplied (hereinafter referred to as a scan line GL_m).

The transistor 852 has a function of controlling whether to write a datasignal by being turned on or off.

One of a pair of electrodes of the capacitor 862 is electricallyconnected to a wiring to which a potential is supplied (hereinafterreferred to as a potential supply line VL_a), and the other iselectrically connected to the other of the source electrode and thedrain electrode of the transistor 852.

The capacitor 862 functions as a storage capacitor for storing writtendata.

One of a source electrode and a drain electrode of the transistor 854 iselectrically connected to the potential supply line VL_a. Further, agate electrode of the transistor 854 is electrically connected to theother of the source electrode and the drain electrode of the transistor852.

One of an anode and a cathode of the light-emitting element 872 iselectrically connected to a potential supply line VL_b, and the other iselectrically connected to the other of the source electrode and thedrain electrode of the transistor 854.

As the light-emitting element 872, the light-emitting element describedin any of Embodiments 1 to 3 can be used.

A high power supply potential VDD is supplied to one of the potentialsupply line VL_a and the potential supply line VL_b, and a low powersupply potential VSS is supplied to the other.

For example, in the display device including the pixel circuit 801 inFIG. 11B, the pixel circuits 801 are sequentially selected row by row bythe gate driver 804 a illustrated in FIG. 11A, whereby the transistor852 is turned on and a data signal is written.

When the transistor 852 is turned off, the pixel circuits 801 in whichthe data has been written are brought into a holding state. Further, theamount of current flowing between the source electrode and the drainelectrode of the transistor 854 is controlled in accordance with thepotential of the written data signal. The light-emitting element 872emits light with a luminance corresponding to the amount of flowingcurrent. This operation is sequentially performed row by row; thus, animage is displayed.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 6

In this embodiment, a display module and electronic devices that includea light-emitting device of one embodiment of the present invention aredescribed with reference to FIG. 12 and FIGS. 13A to 13G.

In a display module 8000 illustrated in FIG. 12, a touch panel 8004connected to an FPC 8003, a display panel 8006 connected to an FPC 8005,a frame 8009, a printed board 8010, and a battery 8011 are providedbetween an upper cover 8001 and a lower cover 8002.

The light-emitting device of one embodiment of the present invention canbe used for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may overlap with the display panel 8006. Alternatively,a counter substrate (sealing substrate) of the display panel 8006 canhave a touch panel function. Alternatively, a photosensor may beprovided in each pixel of the display panel 8006 so as to function as anoptical touch panel.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can function asa radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or a power source using thebattery 8011 provided separately may be used. The battery 8011 can beomitted in the case of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

FIGS. 13A to 13G illustrate electronic devices. These electronic devicescan include a housing 9000, a display portion 9001, a speaker 9003,operation keys 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring or sensing force, displacement, position, speed, acceleration,angular velocity, rotational frequency, distance, light, liquid,magnetism, temperature, chemical substance, sound, time, hardness,electric field, current, voltage, electric power, radiation, flow rate,humidity, gradient, oscillation, odor, or infrared ray), a microphone9008, and the like.

The electronic devices illustrated in FIGS. 13A to 13G can have avariety of functions. For example, a function of displaying a variety ofdata (a still image, a moving image, a text image, and the like) on thedisplay portion, a touch sensor function, a function of displaying acalendar, date, time, and the like, a function of controlling a processwith a variety of software (programs), a wireless communicationfunction, a function of being connected to a variety of computernetworks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a memory medium and displaying the program or data on the displayportion, and the like. Note that functions that can be provided for theelectronic devices illustrated in FIGS. 13A to 13G are not limited tothose described above, and the electronic devices can have a variety offunctions. Although not shown in FIGS. 13A to 13G, the electronic devicemay have a plurality of display portions. The electronic device may havea camera or the like and a function of taking a still image, a functionof taking a moving image, a function of storing the taken image in amemory medium (an external memory medium or a memory medium incorporatedin the camera), a function of displaying the taken image on the displayportion, or the like.

The electronic devices shown in FIGS. 13A to 13G will be described indetail.

FIG. 13A is a perspective view of a portable information terminal 9100.A display portion 9001 of the portable information terminal 9100 isflexible. Therefore, the display portion 9001 can be incorporated alonga bent surface of a bent housing 9000. In addition, the display portion9001 includes a touch sensor, and operation can be performed by touchingthe screen with a finger, a stylus, or the like. For example, when anicon displayed on the display portion 9001 is touched, an applicationcan be started.

FIG. 13B is a perspective view of a portable information terminal 9101.The portable information terminal 9101 functions as, for example, one ormore of a telephone set, a notebook, and an information browsing system.Specifically, the portable information terminal can be used as asmartphone. Note that the speaker 9003, the connection terminal 9006,the sensor 9007, and the like, which are not shown in FIG. 13B, can bepositioned in the portable information terminal 9101 as in the portableinformation terminal 9100 shown in FIG. 13A. The portable informationterminal 9101 can display characters and image information on itsplurality of surfaces. For example, three operation buttons 9050 (alsoreferred to as operation icons, or simply, icons) can be displayed onone surface of the display portion 9001. Furthermore, information 9051indicated by dashed rectangles can be displayed on another surface ofthe display portion 9001. Examples of the information 9051 includedisplay indicating reception of an incoming email, social networkingservice (SNS) message, call, and the like; the title and sender of anemail and SNS message; the date; the time; remaining battery; and thereception strength of an antenna. Instead of the information 9051, theoperation buttons 9050 or the like may be displayed on the positionwhere the information 9051 is displayed.

FIG. 13C is a perspective view of a portable information terminal 9102.The portable information terminal 9102 has a function of displayinginformation on three or more surfaces of the display portion 9001. Here,information 9052, 9053, and 9054 are displayed on different surfaces.For example, a user of the portable information terminal 9102 can seethe display (here, the information 9053) with the portable informationterminal 9102 put in a breast pocket of his/her clothes. Specifically, acaller's phone number, name, or the like of an incoming call isdisplayed in a position that can be seen from above the portableinformation terminal 9102. Thus, the user can see the display withouttaking out the portable information terminal 9102 from the pocket anddecide whether to answer the call.

FIG. 13D is a perspective view of a watch-type portable informationterminal 9200. The portable information terminal 9200 is capable ofexecuting a variety of applications such as mobile phone calls,e-mailing, viewing and editing texts, music reproduction, Internetcommunication, and computer games. The display surface of the displayportion 9001 is bent, and images can be displayed on the bent displaysurface. The portable information terminal 9200 can employ near fieldcommunication that is a communication method based on an existingcommunication standard. In that case, for example, mutual communicationbetween the portable information terminal 9200 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible. The portable information terminal 9200 includes the connectionterminal 9006, and data can be directly transmitted to and received fromanother information terminal via a connector. Power charging through theconnection terminal 9006 is possible. Note that the charging operationmay be performed by wireless power feeding without using the connectionterminal 9006.

FIGS. 13E, 13F, and 13G are perspective views of a foldable portableinformation terminal 9201 that is opened, that is shifted from opened tofolded or from folded to opened, and that is folded, respectively. Thefolded portable information terminal 9201 is highly portable, and theopened portable information terminal 9201 is highly browsable due to aseamless large display region. The display portion 9001 of the portableinformation terminal 9201 is supported by three housings joined togetherby hinges 9055. By folding the portable information terminal 9201 at aconnection portion between two housings 9000 with the hinges 9055, theportable information terminal 9201 can be reversibly changed in shapefrom opened to folded. For example, the portable information terminal9201 can be bent with a radius of curvature of greater than or equal to1 mm and less than or equal to 150 mm.

Electronic devices described in this embodiment are characterized byhaving a display portion for displaying some sort of information. Notethat the light-emitting device of one embodiment of the presentinvention can also be used for an electronic device which does not havea display portion. The display portion of the electronic device of thisembodiment may be non-flexible and display on a flat surface withoutlimitation to the flexible mode capable of displaying along the curvedsurface or the foldable mode.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 7

In this embodiment, examples of lighting devices each using thelight-emitting device of one embodiment of the present invention aredescribed with reference to FIG. 14.

FIG. 14 illustrates an example in which the light-emitting device isused for an interior lighting device 8501. Note that since the area ofthe light-emitting device can be increased, a lighting device having alarge area can also be formed. In addition, a lighting device 8502 inwhich a light-emitting region has a curved surface can also be obtainedwith the use of a housing with a curved surface. A light-emittingelement included in the light-emitting device described in thisembodiment is in a thin film form, which allows the housing to bedesigned more freely. Therefore, the lighting device can be elaboratelydesigned in a variety of ways. Further, a wall of the room may beprovided with a large-sized lighting device 8503. Touch sensors may beprovided in the lighting devices 8501, 8502, and 8503 to control thepower on/off of the lighting devices.

Moreover, when the light-emitting device is used at a surface of atable, a lighting device 8504 which has a function as a table can beobtained. When the light-emitting device is used as part of otherfurniture, a lighting device which has a function as the furniture canbe obtained.

In this manner, a variety of lighting devices to which thelight-emitting device is applied can be obtained. Note that suchlighting devices are also embodiments of the present invention.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1

In this example, an example of fabricating a light-emitting element ofone embodiment of the present invention will be described. FIGS. 15A and15B are a schematic cross-sectional views of light-emitting elements(light-emitting elements 1 to 4) fabricated in this example, Table 1shows the detailed structures of the elements, and structures andabbreviations of compounds used here are given below.

TABLE 1 Structure of light-emitting elements of Example 1 ReferenceThickness Layer numeral (nm) Material Weight ratio Light- Secondelectrode 502 200 Al — emitting Electron-injection 516 1 LiF — element 1layer Electron-transport 515(2) 15 Bphen — layer 515(1) 10 2mDBTBPDBq-II— Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(ppm- 0.8:0.2:0.05emitting layer dmp)₂(acac) First light-emitting 513 10 cgDBCzPA:1,  1:0.02 layer 6mMemFLPAPrn Hole-transport 512 20 PCPPn — layerHole-injection 511 40 DBT3P-II:MoOx 2:1 layer First electrode 501 110ITSO — Light- Second electrode 502 200 Al — emitting Electron-injection516 1 LiF — element 2 layer Electron-transport 515(2) 15 Bphen — layer515(1) 10 2mDBTBPDBq-II — Second light- 514 202mDBTBPDBq-II:PCBBiF:Ir(ppm- 0.8:0.2:0.05 emitting layer dmp)₂(acac)Separation layer 520 2 2mDBTBPDBq- 0.6:0.4 II:PCBBiF Firstlight-emitting 513 10 cgDBCzPA:1,   1:0.02 layer 6mMemFLPAPrnHole-transport 512 20 PCPPn — layer Hole-injection 511 40 DBT3P-II:MoOx2:1 layer First electrode 501 110 ITSO — Light- Second electrode 502 200Al — emitting Electron-injection 516 1 LiF — element 3 layerElectron-transport 515(2) 15 Bphen — layer 515(1) 10 2mDBTBPDBq-II —Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(ppm- 0.5:0.5:0.05 emittinglayer dmp)₂(acac) First light-emitting 513 10 cgDBCzPA:1,   1:0.02 layer6mMemFLPAPrn Hole-transport 512 20 PCPPn — layer Hole-injection 511 40DBT3P-II:MoOx 2:1 layer First electrode 501 110 ITSO — Light- Secondelectrode 502 200 Al — emitting Electron-injection 516 1 LiF — element 4layer Electron-transport 515(2) 15 Bphen — layer 515(1) 10 2mDBTBPDBq-II— Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(ppm- 0.5:0.5:0.05emitting layer dmp)₂(acac) Separation layer 520 2 2mDBTBPDBq-II:PCBBiF0.6:0.4 First light-emitting 513 10 cgDBCzPA:1,   1:0.02 layer6mMemFLPAPrn Hole-transport 512 20 PCPPn — layer Hole-injection 511 40DBT3P-II:MoOx 2:1 layer First electrode 501 110 ITSO —<1-1. Fabrication of Light-Emitting Element 1>

Indium tin oxide containing silicon oxide (indium tin oxide doped withSiO₂: ITSO) which was formed over a glass substrate 500 to have athickness of 110 nm and an area of 2 mm×2 mm was used as a firstelectrode 501. On the first electrode 501,1,3,5-tri(dibenzothiophen-4-yl)benzene (DBT3P-II) and molybdenum oxide(MoO₃) were deposited by co-evaporation in a weight ratio ofDBT3P-II:MoO₃=2:1 to a thickness of 40 nm, so that a hole-injectionlayer 511 was formed. Note that co-evaporation is an evaporation methodin which a plurality of different substances is concurrently vaporizedfrom different evaporation sources.

On the hole-injection layer 511,3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (PCPPn) was depositedby evaporation to a thickness of 20 nm, so that a hole-transport layer512 was formed.

On the hole-transport layer 512,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (cgDBCzPA),andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(1,6mMemFLPAPrn) were deposited by co-evaporation in a weight ratio ofcgDBCzPA:1,6mMemFLPAPrn=1:0.02 to a thickness of 10 nm, so that thefirst light-emitting layer 513 was formed. Note that cgDBCzPA was thehost material and 1,6mMemFLPAPrn was the fluorescent material (the guestmaterial) in the first light-emitting layer 513.

On the first light-emitting layer 513,2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine(PCBBiF), andbis{2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κO,O′)iridium(III)(Ir(ppm-dmp)₂(acac)) were deposited by co-evaporation in a weight ratioof 2mDBTBPDBq-II:PCBBiF:Ir(ppm-dpm)₂(acac)=0.8:0.2:0.05 to a thicknessof 20 nm, so that the second light-emitting layer 514 was formed. Notethat 2mDBTBPDBq-II was the first organic compound (the host material),PCBBiF was the second organic compound (the assist material), andIr(ppm-dmp)₂(acac) was the phosphorescent material (the guest material)in the second light-emitting layer 514.

On the second light-emitting layer 514, 2mDBTBPDBq-II andbathophenanthroline (Bphen) were sequentially deposited by evaporationto a thickness of 10 nm and 15 nm, respectively, so thatelectron-transport layers 515(1) and 512(2) were formed. On theelectron-transport layers 515(1) and 515(2), lithium fluoride wasdeposited by evaporation to a thickness of 1 nm to form theelectron-injection layer 516. Furthermore, aluminum was deposited byevaporation to a thickness of 200 nm to form the second electrode 502.

Next, a sealing glass substrate was fixed to the glass substrate using asealing member in a glove box containing a nitrogen atmosphere. In thismanner, the light-emitting element was sealed. Note that for sealing,the sealing member was applied to surround the light-emitting element,irradiation with 365-nm ultraviolet light at 6 J/cm² was performed, andheat treatment was performed at 80° C. for 1 hour. Through the abovesteps, the light-emitting element 1 was obtained.

<1-2. Fabrication of Light-Emitting Element 2>

Similar to the light emitting element 1, on the first electrode 501,DBT3P-II and molybdenum oxide (MoO₃) were deposited by co-evaporation ina weight ratio of DBT3P-II:MoO₃=2:1 to a thickness of 40 nm, so that thehole-injection layer 511 was formed.

On the hole-injection layer 511, PCPPn was deposited by evaporation to athickness of 20 nm, so that the hole-transport layer 512 was formed.

On the hole-transport layer 512, cgDBCzPA and 1,6mMemFLPAPrn weredeposited by co-evaporation in a weight ratio ofcgDBCzPA:1,6mMemFLPAPrn=1:0.02 to a thickness of 10 nm, so that thefirst light-emitting layer 513 was formed.

On the first light-emitting layer 513, 2mDBTBPDBq-II and PCBBiF weredeposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF=0.6:0.4 to a thickness of 2 nm, so that theseparation layer 520 was formed.

On the separation layer 520, 2mDBTBPDBq-II, PCBBiF, andIr(ppm-dmp)₂(acac) were deposited by co-evaporation in weight ratio of2mDBTBPDBq-II:PCBBiF:Ir(ppm-dmp)₂(acac)=0.8:0.2:0.05 to a thickness of20 nm, so that the second light-emitting layer 514 was formed.

On the second light-emitting layer 514, 2mDBTBPDBq-II and Bphen weresequentially deposited by evaporation to a thickness of 10 nm and 15 nm,respectively, so that electron-transport layers 515(1) and 512(2) wereformed. On the electron-transport layers 515(1) and 515(2), lithiumfluoride was deposited by evaporation to a thickness of 1 nm to form theelectron-injection layer 516. Furthermore, aluminum was deposited byevaporation to a thickness of 200 nm to form the second electrode 502.

Next, a sealing glass substrate was fixed to the glass substrate using asealing member in a glove box containing a nitrogen atmosphere to sealthe light-emitting element. In this manner, the light-emitting element 2was obtained. As the sealing method, a method similar to that used forthe light-emitting element 1 was used.

<1-3. Fabrication of Light-Emitting Element 3>

The light-emitting element 3 was fabricated through the same steps asthose for the above-mentioned light-emitting element 1 except stepsmentioned below.

On the first light-emitting layer 513,2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine(PCBBiF), andbis{2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κO,O′)iridium(III)Ir(ppm-dmp)₂(acac) were deposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF:Ir(ppm-dpm)₂(acac)=0.5:0.5:0.05 to a thickness of20 nm, so that the second light-emitting layer 514 was formed.

<1-4. Fabrication of Light-Emitting Element 4>

The light-emitting element 4 was fabricated through the same steps asthose for the above-mentioned light-emitting element 2 except stepsmentioned below.

On the separation layer 520,2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(2mDBTBPDBq-H),N-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine(PCBBiF), and bis{2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κO,O′)iridium(III)Ir(ppm-dmp)₂(acac) were deposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF:Ir(ppm-dpm)₂(acac)=0.5:0.5:0.05 to a thickness of20 nm, so that the second light-emitting layer 514 was formed.

It is to be noted that an evaporation method using resistive heating wasemployed for all the evaporation steps.

<1-5. Characteristics of Light-Emitting Elements 1 to 4>

FIG. 16A shows current density-luminance characteristics of thelight-emitting elements 1 to 4. In FIG. 16A, the horizontal axisrepresents current density (mA/cm²) and the vertical axis representsluminance (cd/m²). FIG. 16B shows voltage-luminance characteristics ofthe light-emitting elements 1 to 4. In FIG. 16B, the horizontal axisrepresents voltage (V) and the vertical axis represents luminance(cd/m²). FIG. 17A shows luminance-power efficiency characteristics ofthe light-emitting elements 1 to 4. In FIG. 17A, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents powerefficiency (lm/W). FIG. 17B shows luminance-current efficiencycharacteristics of the light-emitting elements 1 to 4. In FIG. 17B, thehorizontal axis represents luminance (cd/m²) and the vertical axisrepresents current efficiency (cd/A). Note that the measurement for eachlight-emitting element was carried out at room temperature (in theatmosphere maintained at 25° C.).

Table 2 shows element characteristics of the light-emitting elements 1to 4 at around 1000 cd/m².

TABLE 2 Element characteristics of light-emitting elements of Example 1External Current Current Power quantum Voltage Current densityChromaticity Luminance efficiency efficiency efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 3.1 0.15 3.8 (0.30,0.34) 910 24 24 10 emitting element 1 Light- 3.1 0.14 3.4 (0.32, 0.37)960 28 29 11 emitting element 2 Light- 3.1 0.093 2.3 (0.37, 0.44) 870 3738 12 emitting element 3 Light- 3.2 0.12 3.0 (0.38, 0.45) 1200 40 39 13emitting element 4

FIG. 18 shows emission spectra when a current at a current density of2.5 mA/cm² was supplied to the light-emitting elements 1 to 4. As shownin FIG. 18, each spectrum of the light-emitting elements 1 to 4 haspeaks at the blue wavelength region and the yellow wavelength region;therefore, it is found that the two light-emitting materials in eachlight-emitting element emitted light at a time.

As shown in Table 1, difference between the light-emitting elements 1and 2 was whether with or without the separation layer 520, anddifference between the light-emitting elements 3 and 4 was whether withor without the separation layer 520. On the basis of the results shownin FIGS. 16A and 16B and FIGS. 17A and 17B, the light-emitting elements1 and 2 had approximately the same element characteristics regardless ofwhether with or without the separation layer 520. In addition, on thebasis of the results shown in FIGS. 16A and 16B and FIGS. 17A and 17B,the light-emitting elements 3 and 4 had approximately the same elementcharacteristics regardless of whether with or without the separationlayer 520. The concentration of PCBBiF, which was the second organiccompound (the assist material) of the second light-emitting layer 514 ofthe light-emitting elements 3 and 4, was high in the light-emittingelements 3 and 4 as compared with that in the light-emitting elements 1and 2. Thus, the intensity of the yellow spectrum was increased.Therefore, it is found that the intensity of the yellow spectrum can beeasily adjusted while the element characteristics having high efficiencyare kept. In addition, on the basis of the results shown in FIG. 18, itis found that, in the light-emitting elements 1 and 2, the intensity ofthe blue and yellow emission spectra can be adjusted by the presence orabsence of the separation layer 520.

The structures described in this example can be used in an appropriatecombination with any of the structures described in the otherembodiments and examples.

Example 2

In this example, an example of fabricating a light-emitting element ofone embodiment of the present invention will be described. FIG. 15B is aschematic cross-sectional view of a light-emitting element (alight-emitting element 5) fabricated in this example, and Table 3 showsthe detailed structure of the element, and structures and names ofcompounds used here are given below. Note that the structures and namesof the compounds used for the light-emitting elements 1 to 4 describedin Example 1 are not given here.

TABLE 3 Structure of light-emitting element of Example 2 ReferenceThickness Layer numeral (nm) Material Weight ratio Light- Secondelectrode 502 200 Al — emitting Electron-injection 516 1 LiF — element 5layer Electron-transport 515(2) 15 Bphen — layer 515(1) 10 2mDBTBPDBq-II— Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(dmppm- 0.8:0.2:0.05emitting layer dmp)₂(acac) Separation layer 520 2 2mDBTBPDBq-II:PCBBiF0.6:0.4 First light-emitting 513 5 cgDBCzPA:1,   1:0.03 layer 6FrAPrn-IIHole-transport layer 512 20 PCPPn — Hole-injection layer 511 20DBT3P-II:MoOx 2:1 First electrode 501 110 ITSO —<2-1. Fabrication of Light-Emitting Element 5>

Similar to the light emitting element 1, on the first electrode 501,DBT3P-II and molybdenum oxide (MoO₃) were deposited by co-evaporation ina weight ratio of DBT3P-II:MoO₃=2:1 to a thickness of 20 nm, so that thehole-injection layer 511 was formed.

On the hole-injection layer 511, PCPPn was deposited by evaporation to athickness of 20 nm, so that the hole-transport layer 512 was formed.

On the hole-transport layer 512, cgDBCzPA andN,N′-bis(dibenzofuran-4-yl)-N,N′-diphenylpyrene-1,6-diamine(1,6FrAPrn-II) were deposited by co-evaporation in a weight ratio ofcgDBCzPA:1,6FrAPrn-II=1:0.03 to a thickness of 5 nm, so that the firstlight-emitting layer 513 was formed. Note that cgDBCzPA was the hostmaterial and 1,6FrAPrn-II was the fluorescent material (the guestmaterial) in the first light-emitting layer 513.

On the first light-emitting layer 513, 2mDBTBPDBq-II and PCBBiF weredeposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF=0.6:0.4 to a thickness of 2 nm, so that theseparation layer 520 was formed.

On the separation layer 520, 2mDBTBPDBq-II, PCBBiF, andbis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κ²O,O′)iridium(III)(Ir(dmppm-dmp)₂(acac)) were deposited by co-evaporation in a weightratio of 2mDBTBPDBq-II:PCBBiF:Ir(dmppm-dmp)₂(acac)=0.8:0.2:0.05 to athickness of 20 nm, so that the second light-emitting layer 514 wasformed. Note that 2mDBTBPDBq-II was the first organic compound (the hostmaterial), PCBBiF was the second organic compound (the assist material),and Ir(dmppm-dmp)₂(acac) was the phosphorescent material (the guestmaterial) in the second light-emitting layer 514.

On the second light-emitting layer 514, 2mDBTBPDBq-II and Bphen weresequentially deposited by evaporation to a thickness of 10 nm and 15 nm,respectively, so that electron-transport layers 515(1) and 512(2) wereformed. On the electron-transport layers 515(1) and 515(2), lithiumfluoride was deposited by evaporation to a thickness of 1 nm to form theelectron-injection layer 516. Furthermore, aluminum was deposited byevaporation to a thickness of 200 nm to form the second electrode 502.

It is to be noted that an evaporation method using resistive heating wasemployed for all the evaporation steps.

Next, a sealing glass substrate was fixed to the glass substrate using asealing member in a glove box containing a nitrogen atmosphere to sealthe light-emitting element. In this manner, the light-emitting element 5was obtained. As the sealing method, a method similar to that used forthe light-emitting element 1 was used.

<2-2. Characteristics of Light-Emitting Element 5>

FIG. 19A shows current density-luminance characteristics of thelight-emitting element 5. In FIG. 19A, the horizontal axis representscurrent density (mA/cm²) and the vertical axis represents luminance(cd/m²). FIG. 19B shows the voltage-luminance characteristics of thelight-emitting element 5. In FIG. 19B, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). FIG. 20Ashows luminance-power efficiency characteristics of the light-emittingelement 5. In FIG. 20A, the horizontal axis represents luminance (cd/m²)and the vertical axis represents power efficiency (lm/W). FIG. 20B showsluminance-current efficiency characteristics of the light-emittingelement 5. In FIG. 20B, the horizontal axis represents luminance (cd/m²)and the vertical axis represents current efficiency (cd/A). Note thatthe measurement for the light-emitting element was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

Further, Table 4 shows the element characteristics of the light-emittingelement 5 at around 1000 cd/m².

TABLE 4 Element characteristics of light-emitting element of Example 2External Current Current Power quantum Voltage Current densityChromaticity Luminance efficiency efficiency efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.9 0.062 1.5 (0.47,0.45) 870 56 61 18 emitting element 5

FIG. 21 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 5. As shown inFIG. 21, the spectrum of the light-emitting element 5 has peaks at theblue wavelength region and the yellow wavelength region; therefore, itis found that the two light-emitting materials therein emitted light ata time.

The light-emitting element 5 of this example was different from thelight-emitting elements 1 to 4 of Example 1 in the fluorescent materialof the first light-emitting layer 513 and the phosphorescent material ofthe second light-emitting layer 514. On the basis of the results shownin FIGS. 19A and 19B and FIGS. 20A and 20B, it is found that thelight-emitting element 5 had element characteristics with highefficiency, similar to the light-emitting elements 1 to 4 of Example 1.The correlated color temperature of the light-emitting element 5 was2850 K at around 1000 cd/m². Therefore, it can be used also for alighting purpose.

The structures described in this example can be used in an appropriatecombination with any of the structures described in the otherembodiments and examples.

Example 3

In this example, an example of fabricating a light-emitting element ofone embodiment of the present invention will be described. FIG. 15B is aschematic cross-sectional view of a light-emitting element (alight-emitting element 6) fabricated in this example, and Table 5 showsthe detailed structure of the element, and a structure and a name of acompound used here are given below. Note that the structures and namesof the compounds used for the light-emitting elements 1 to 4 describedin Example 1 are not given below.

TABLE 5 Structure of light-emitting element of Example 3 ReferenceThickness Weight Layer numeral (nm) Material ratio Light- Second 502 200Al — emitting electrode element 6 Electron- 516 1 LiF — injection layerElectron- 515(2) 15 Bphen — transport layer 515(1) 10 2mDBTBPDBq-II —Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.05emitting layer Separation 520 2 2mDBTBPDBq-II:PCBBiF 0.6:0.4 layer Firstlight- 513 5 cgDBCzPA:1,   1:0.03 emitting layer 6mMemFLPAPrnHole-transport 512 20 PCPPn — layer Hole-injection 511 20 DBT3P-II:MoOx2:1 layer First electrode 501 110 ITSO —<3-1. Fabrication of Light-Emitting Element 6>

Similar to the light emitting element 1, on the first electrode 501,DBT3P-II and molybdenum oxide (MoO₃) were deposited by co-evaporation ina weight ratio of DBT3P-II:MoO₃=2:1 to a thickness of 20 nm, so that thehole-injection layer 511 was formed.

On the hole-injection layer 511, PCPPn was deposited by evaporation to athickness of 20 nm, so that the hole-transport layer 512 was formed.

On the hole-transport layer 512, cgDBCzPA and 1,6mMemFLPAPrn weredeposited by co-evaporation in a weight ratio ofcgDBCzPA:1,6mMemFLPAPrn=1:0.03 to a thickness of 5 nm, so that the firstlight-emitting layer 513 was formed.

On the first light-emitting layer 513, 2mDBTBPDBq-II and PCBBiF weredeposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF=0.6:0.4 to a thickness of 2 nm, so that theseparation layer 520 was formed.

On the separation layer 520, 2mDBTBPDBq-II, PCBBiF, and(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(another name:bis{2-[5-methyl-6-(2-methylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κ²O,O′)iridium(III))(Ir(mpmppm)₂(acac)) were deposited by co-evaporation in a weight ratioof 2mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac)=0.8:0.2:0.05 to a thickness of20 nm, so that the second light-emitting layer 514 was formed. Note that2mDBTBPDBq-II was the first organic compound (the host material), PCBBiFwas the second organic compound (the assist material), andIr(mpmppm)₂(acac) was the phosphorescent material (the guest material)in the second light-emitting layer 514.

On the second light-emitting layer 514, 2mDBTBPDBq-II and Bphen weresequentially deposited by evaporation to a thickness of 10 nm and 15 nm,respectively, so that electron-transport layers 515(1) and 512(2) wereformed. On the electron-transport layers 515(1) and 515(2), lithiumfluoride was deposited by evaporation to a thickness of 1 nm to form theelectron-injection layer 516. Furthermore, aluminum was deposited byevaporation to a thickness of 200 nm to form the second electrode 502.

It is to be noted that an evaporation method using resistive heating wasemployed for all the evaporation steps.

Next, a sealing glass substrate was fixed to the glass substrate using asealing member in a glove box containing a nitrogen atmosphere to sealthe light-emitting element. In this manner, the light-emitting element 6was obtained. As the sealing method, a method similar to that used forthe light-emitting element 1 was used.

<3-2. Characteristics of Light-Emitting Element 6>

FIG. 22A shows current density-luminance characteristics of thelight-emitting element 6. In FIG. 22A, the horizontal axis representscurrent density (mA/cm²) and the vertical axis represents luminance(cd/m²). FIG. 22B shows the voltage-luminance characteristics of thelight-emitting element 6. In FIG. 22B, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). FIG. 23Ashows luminance-power efficiency characteristics of the light-emittingelement 6. In FIG. 23A, the horizontal axis represents luminance (cd/m²)and the vertical axis represents power efficiency (lm/W). FIG. 23B showsluminance-current efficiency characteristics of the light-emittingelement 6. In FIG. 23B, the horizontal axis represents luminance (cd/m²)and the vertical axis represents current efficiency (cd/A). Note thatthe measurement for the light-emitting element was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

Further, Table 6 shows the element characteristics of the light-emittingelement 6 at around 1000 cd/m².

TABLE 6 Element characteristics of light-emitting element of Example 3External Current Current Power quantum Voltage Current densityChromaticity Luminance efficiency efficiency efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.9 0.055 1.4 (0.46,0.47) 790 58 62 19 emitting element 6

FIG. 24 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 6. As shown inFIG. 24, the spectrum of the light-emitting element 6 has peaks at theblue wavelength region and the yellow wavelength region; therefore, itis found that the two light-emitting materials therein emit light at atime.

The light-emitting element 6 of this example is different from thelight-emitting elements 1 to 4 of Example 1 in the phosphorescentmaterial of the second light-emitting layer 514. On the basis of theresults shown in FIGS. 22A and 22B and FIGS. 23A and 23B, it is foundthat the light-emitting element 6 has element characteristics with highefficiency, similar to the light-emitting elements 1 to 4 of Example 1.The correlated color temperature of the light-emitting element 6 was3090 K at around 1000 cd/m². Therefore, it can be used also for alighting purpose.

The structures described in this example can be used in an appropriatecombination with any of the structures described in the otherembodiments and examples.

Example 4

In this example, an example of fabricating a light-emitting element ofone embodiment of the present invention will be described. FIG. 25 is aschematic cross-sectional view of light-emitting elements(light-emitting elements 7 to 10) fabricated in this example, and Table7 shows the detailed structures of the elements. Note that thestructures of compounds used for the light-emitting elements 7 to 10 arethe same as those of the compounds used for the light-emitting elements1 to 6; thus the descriptions thereof are omitted.

TABLE 7 Structure of light-emitting element of Example 4 ReferenceThickness Layer numeral (nm) Material Weight ratio Light-emitting — 5522360 CF(Red) — Element 7 Second electrode 502(2) 70 ITO — 502(1) 15Ag:Mg 0.5:0.05*¹⁾ Electron-injection 516 1 LiF — layerElectron-transport 515(2) 20 Bphen — layer 515(1) 15 2mDBTBPDBq-II —Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.06emitting layer Separation layer 520 2 2mDBTBPDBq-II:PCBBiF 0.2:0.3 Firstlight-emitting 513 10 cgDBCzPA:1,   1:0.02 layer 6mMemFLPAPrnHole-transport 512 20 PCPPn — layer Hole-injection 511 87.5DBT3P-II:MoOx   2:1 layer First electrode 501(3) 75 ITSO — 501(2) 6 Ti —501(1) 200 Al—Ni—La — Light-emitting — 552 1290 CF(Green) — Element 8Second electrode 502(2) 70 ITO — 502(1) 15 Ag:Mg 0.5:0.05*¹⁾Electron-injection 516 1 LiF — layer Electron-transport 515(2) 20 Bphen— layer 515(1) 15 2mDBTBPDBq-II — Second light- 514 202mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.06 emitting layerSeparation layer 520 2 2mDBTBPDBq-II:PCBBiF 0.2:0.3 First light-emitting513 10 cgDBCzPA:1,   1:0.02 layer 6mMemFLPAPrn Hole-transport 512 20PCPPn — layer Hole-injection 511 57.5 DBT3P-II:MoOx   2:1 layer Firstelectrode 501(3) 75 ITSO — 501(2) 6 Ti — 501(1) 200 Al—Ni—La —Light-emitting — 552 780 CF(Blue) — Element 9 Second electrode 502(2) 70ITO — 502(1) 15 Ag:Mg 0.5:0.05*¹⁾ Electron-injection 516 1 LiF — layerElectron-transport 515(2) 20 Bphen — layer 515(1) 15 2mDBTBPDBq-II —Second light- 514 20 2mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.06emitting layer Separation layer 520 2 2mDBTBPDBq-II:PCBBiF 0.2:0.3 Firstlight-emitting 513 10 cgDBCzPA:1,   1:0.02 layer 6mMemFLPAPrnHole-transport 512 20 PCPPn — layer Hole-injection 511 50 DBT3P-II:MoOx  2:1 layer First electrode 501(3) 40 ITSO — 501(2) 6 Ti — 501(1) 200Al—Ni—La — Light-emitting — 552 800 CF(Yellow) — Element 10 Secondelectrode 502(2) 70 ITO — 502(1) 15 Ag:Mg 0.5:0.05*¹⁾ Electron-injection516 1 LiF — layer Electron-transport 515(2) 20 Bphen — layer 515(1) 152mDBTBPDBq-II — Second light- 514 202mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.06 emitting layerseparation layer 520 2 2mDBTBPDBq-II:PCBBiF 0.2:0.3 First light-emitting513 10 cgDBCzPA:1,   1:0.02 layer 6mMemFLPAPrn Hole-transport 512 20PCPPn — layer Hole-injection 511 65 DBT3P-II:MoOx   2:1 layer Firstelectrode 501(3) 75 ITSO — 501(2) 6 Ti — 501(1) 200 Al—Ni—La — ^(*1))Theratio of Ag:Mg is described by the volume ratio.<4-1. Fabrication of Light-Emitting Elements 7 to 10>

On the glass substrate 500, an alloy film (Al—Ni—La) of aluminum (Al),nickel (Ni), and lanthanum (La) was formed by a sputtering method to athickness of 200 nm as a first electrode 501(1). Next, a titanium (Ti)film was formed by a sputtering method to a thickness of 6 nm and heatedat 300° C. for 1 hour to form a film including a titanium oxide as afirst electrode 501(2). Next, as a first electrode 501(3), an indium tinoxide film containing silicon oxide (ITSO) was formed by a sputteringmethod. Note that the first electrodes 501(1), 501(2), and 501(3) formedthe first electrode 501, and the electrode area of the first electrode501 was 2 mm×2 mm.

The film thickness of the first electrode 501(3) in each of the lightemitting elements 7, 8, and 10 was 75 nm, while the film thickness ofthe first electrode 501(3) in the light emitting element 9 was 40 nm.

Next, on the first electrode 501(3), DBT3P-II and molybdenum oxide(MoO₃) were deposited by co-evaporation in a weight ratio ofDBT3P-II:MoO₃=2:1, so that the hole-injection layer 511 was formed.

The film thickness of the hole-injection layer 511 in the light-emittingelement 7, that in the light-emitting element 8, that in thelight-emitting element 9, and that in the light-emitting element 10 were87.5 nm, 57.5 nm, 50 nm, and 65 nm, respectively.

Next, on the hole-injection layer 511, PCPPn was deposited byevaporation to a thickness of 20 nm, so that the hole-transport layer512 was formed.

On the hole-transport layer 512, cgDBCzPA and 1,6mMemFLPAPrn weredeposited by co-evaporation in a weight ratio ofcgDBCzPA:1,6mMemFLPAPrn=1:0.02 to a thickness of 10 nm, so that thefirst light-emitting layer 513 was formed.

On the first light-emitting layer 513, 2mDBTBPDBq-II and PCBBiF weredeposited by co-evaporation in a weight ratio of2mDBTBPDBq-II:PCBBiF=0.2:0.3 to a thickness of 2 nm, so that theseparation layer 520 was formed.

On the separation layer 520, 2mDBTBPDBq-II, PCBBiF, andIr(mpmppm)₂(acac) were deposited by co-evaporation in weight ratio of2mDBTBPDBq-II:PCBBiF:Ir(mpmppm)₂(acac)=0.8:0.2:0.06 to a thickness of 20nm, so that the second light-emitting layer 514 was formed.

On the second light-emitting layer 514, 2mDBTBPDBq-II and Bphen weresequentially deposited by evaporation to a thickness of 15 nm and 20 nm,respectively, so that electron-transport layers 515(1) and 512(2) wereformed. On the electron-transport layers 515(1) and 515(2), lithiumfluoride was deposited by evaporation to a thickness of 1 nm to form theelectron-injection layer 516.

On the electron-injection layer 516, an alloy film of silver (Ag) andmagnesium (Mg) was deposited by co-evaporation in a volume ratio ofAg:Mg=0.5:0.05 to a thickness of 15 nm, so that the second electrode502(1) was formed.

Next, on the second electrode 502(1), an ITO film was formed by asputtering method to a thickness of 70 nm.

As shown in Table 7, as a coloring layer 552 on a sealing substrate 550,a red (R) color filter with a thickness of 2.36 μm, a green (G) colorfilter with a thickness of 1.29 μm, a blue (B) color filter with athickness of 0.78 μm, and a yellow (Y) color filter with a thickness of0.80 μm were formed in the light-emitting elements 7, 8, 9, and 10,respectively.

Each of the light-emitting elements 7 to 10 formed as described aboveand the corresponding sealing substrate formed as described above wereattached with each other to be sealed in a glove box containing anitrogen atmosphere without exposed to an air atmosphere (the sealingmember was applied to surround the element, irradiation with 365-nmultraviolet light at 6 J/cm² was performed, and heat treatment wasperformed at 80° C. for 1 hour).

It is to be noted that an evaporation method using resistive heating wasemployed for all the evaporation steps.

<4-2. Characteristics of Light-Emitting Elements 7 to 10>

FIG. 26A shows current density-luminance characteristics of thelight-emitting elements 7 to 10. In FIG. 26A, the horizontal axisrepresents current density (mA/cm²) and the vertical axis representsluminance (cd/m²). FIG. 26B shows the voltage-luminance characteristicsof the light-emitting elements 7 to 10. In FIG. 26B, the horizontal axisrepresents voltage (V) and the vertical axis represents luminance(cd/m²). Note that the measurement for each of the light-emittingelements was carried out at room temperature (under an atmosphere inwhich the temperature was kept at 25° C.).

Further, Table 8 shows the element characteristics of the light-emittingelements 7 to 10 at around 1000 cd/m².

TABLE 8 Element characteristics of light-emitting elements of Example 4Current Current Voltage Current density Chromaticity Luminanceefficiency (V) (mA) (mA/cm²) (x, y) (cd/m²) (cd/A) Light-emitting 3.70.64 16 (0.66, 0.34) 930 5.8 element 7 Light-emitting 3.1 0.12 3.2(0.33, 0.64) 850 27 element 8 Light-emitting 4.8 2.4 61 (0.14, 0.055)1000 1.6 element 9 Light-emitting 3.0 0.078 2.0 (0.41, 0.58) 810 41element 10

FIG. 27 shows emission spectra when a current at a current density of2.5 mA/cm² was supplied to the light-emitting elements 7 to 10. FIG. 27shows that the spectrum of the light-emitting element 7 has a peak inthe red wavelength region, that the spectrum of the light-emittingelement 8 has a peak in the green wavelength region, that the spectrumof the light-emitting element 9 has a peak in the blue wavelengthregion, and that the spectrum of the light-emitting element 10 has apeak in the yellow wavelength region. Thus, when the light-emittingelements 7 to 10 are used in combination, full-color display can beachieved.

As shown in Table 7, the light-emitting elements 7 to 10 fabricated inthis example each included the same first light-emitting layer 513 andthe same second light-emitting layer 514. As shown in FIGS. 26A and 26Band FIG. 27, even when the structure of the first light-emitting layer513 and the second light-emitting layer 514 were common in thelight-emitting elements, the light-emitting elements each of whichemitted light with a different emission spectrum from the others hadhigh current efficiency and excellent element characteristics.

The structures described in this example can be used in an appropriatecombination with any of the structures described in the otherembodiments and examples.

Reference Example

A synthesis method of Ir(ppm-dmp)₂(acac) used in Examples 1 and 2 willbe described. The synthesis scheme is shown below.

1. Synthesis of 4-chloro-6-phenylpyrimidine

A mixture of 5.0 g of 4,6-dichloropyrimidine, 4.9 g of phenylboronicacid, 7.1 g of sodium carbonate, 0.34 g ofbis(triphenylphosphine)palladium(II)dichloride (Pd (PPh₃)₂Cl₂), 20 mL ofacetonitrile, and 20 mL of water was heated to reflux by irradiationwith microwaves (2.45 GHz, 100 W) under an argon stream for 1 hour. Theobtained mixture was subjected to extraction with dichloromethane andpurified by silica gel column chromatography (developing solvent:dichloromethane), whereby 1.6 g of 4-chloro-6-phenylpyrimidine wasobtained (yield: 23%, a pale yellow solid). Note that the microwaveirradiation in this reference example was performed using a microwavesynthesis system (Discover, manufactured by CEM Corporation).

2. Synthesis of 4-phenyl-6-(2,6-dimethylphenyl)pyrimidine (Hppm-dmp)

A mixture of 1.6 g of 4-chloro-6-phenylpyrimidine, 1.5 g of2,6-dimethylphenylboronic acid, 1.8 g of sodium carbonate, 59 mg of Pd(PPh₃)₂Cl₂, 20 mL of N,N-dimethylformamide, and 20 mL of water washeated to reflux by irradiation with microwaves (2.45 GHz, 100 W) underan argon stream for 2 hours. The obtained mixture was subjected toextraction with dichloromethane and purified by silica gel columnchromatography (developing solvent: ethyl acetate and hexane in a ratioof 1:5), whereby 0.50 g of Hppm-dmp was obtained (yield: 23%, a paleyellow oily substance).

3. Synthesis ofDi-μ-chloro-tetrakis{2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}diiridium(III)([Ir(ppm-dmp)₂Cl]₂)

A mixture of 1.0 g of Hppm-dmp, 0.57 g of iridium(III) chloride hydrate,20 mL of 2-ethoxyethanol, and 20 mL of water was heated to reflux byirradiation with microwaves (2.45 GHz, 100 W) under an argon stream for3 hours. The obtained mixture was filtrated and the resulting solid waswashed with methanol, whereby 1.1 g of [Ir(ppm-dmp)₂Cl]₂ was obtained(yield: 74%, an orange solid).

4. Synthesis of Ir(ppm-dmp)₂(acac)

A mixture of 1.1 g of [Ir(ppm-dmp)₂Cl]₂, 0.77 g of sodium carbonate,0.23 g of acetylacetone (Hacac), and 30 mL of 2-ethoxyethanol was heatedto reflux by irradiation with microwaves (2.45 GHz, 120 W) under anargon stream for 2 hours. The obtained mixture was filtrated, and aninsoluble was washed with methanol. The obtained filtrate wasconcentrated, a residue was purified by silica gel column chromatography(developing solvent: ethyl acetate and hexane in a ratio of 1:5), andthe obtained solid was recrystallized from hexane, wherebyIr(ppm-dmp)₂(acac) was obtained (yield: 59%, an orange powdered solid).By a train sublimation method, 0.21 g of the obtained orange powderedsolid were purified, whereby the objective orange solid was collected ina yield of 48%. The conditions of the purification by sublimation wereas follows: the pressure was 2.7 Pa; the flow rate of an argon gas was5.0 mL/min; and the temperature was 240° C. ¹H-NMR (nuclear magneticresonance) spectrum data of the obtained Ir(ppm-dmp)₂(acac) are shownbelow.

¹H-NMR. δ (CDCl₃): 1.85 (s, 6H), 2.26 (s, 12H), 5.35 (s, 1H), 6.46-6.48(dd, 2H), 6.83-6.90 (dm, 4H), 7.20-7.22 (d, 4H), 7.29-7.32 (t, 2H),7.63-7.65 (dd, 2H), 7.72 (ds, 2H), 9.24 (ds, 2H).

Example 5

In this example, described are a fabrication example of a light-emittingelement 11 not including the second light-emitting layer but includingthe first light-emitting layer of the light-emitting element of oneembodiment of the present invention, and a formation example of alight-emitting element 12 not including the first light-emitting layerbut including the second light-emitting layer of the light-emittingelement of one embodiment of the present invention. A structure ofN,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPrn-03) which is a compound used in this exampleis given below. The structures and names of the compounds used for thelight-emitting elements in the above-described examples are not givenbelow.

5-1. Fabrication of Light-Emitting Elements 11 and 12

Similar to the light-emitting element 1 described in Example 1, thelight-emitting element 11 has a structure in which the hole-injectionlayer 511, the hole-transport layer 512, and the first light-emittinglayer 513 are stacked over the first electrode 501; however, the secondlight-emitting layer 514 is not formed and the electron-transport layers515(1) and 515(2), the electron-injection layer 516, and the secondelectrode 502 are stacked over the first light-emitting layer 513 inthis order. Similar to the light-emitting element 1 described in Example1, the light-emitting element 12 has a structure in which thehole-injection layer 511 and the hole-transport layer 512 are stackedover the first electrode 501; however, the first light-emitting layer513 is not formed and the second light-emitting layer 514, theelectron-transport layers 515(1) and 515(2), the electron-injectionlayer 516, and the second electrode 502 are stacked over thehole-transport layer 512 in this order.

Thus, Example 1 is referred to for the specific fabrication method ofthe light-emitting elements. Table 9 shows the specific elementstructures of the light-emitting elements fabricated in this example(the light-emitting elements 11 and 12).

TABLE 9 Structure of light-emitting elements of Example 5 ReferenceThickness Weight Layer numeral (nm) Material ratio Light- Second 502 200Al — emitting electrode Element Electron- 516 1 LiF — 11 injection layerElectron- 515(2) 15 Bphen — transport 515(1) 10 cgDBCzPA — layer Firstlight- 513 25 cgDBCzPA:1, 1:0.03 emitting 6BnfAPrn-03 layer Hole- 512 30PCPPn — transport layer Hole- 511 10 PCPPn:MoOx 4:2 injection layerFirst 501 110 ITSO — electrode Light- Second 502 130 Al — emittingelectrode Element Electron- 516 1 LiF — 12 injection layer Electron-515(2) 20 Bphen — transport 515(1) 15 2mDBTBPDBqII — layer Second 514 402mDBTBPDBqII:PCBBiF:Ir(mpmppm)₂(acac) 0.8:0.2:0.06 light- emitting layerHole- 512 20 BPAFLP — transport layer Hole- 511 10 DBT3PII:MoOx 1:0.5injection layer First 501 110 ITSO — electrode

5-2. Characteristics of Light-Emitting Elements 11 and 12

FIG. 28 shows luminance-external quantum efficiency characteristics ofthe light-emitting element 11. FIG. 31 shows luminance-external quantumefficiency characteristics of the light-emitting element 12. In each ofFIG. 28 and FIG. 31, the horizontal axis represents luminance (cd/m²)and the vertical axis represents external quantum efficiency (%). Notethat the measurement of each of the light-emitting elements was carriedout at room temperature (under an atmosphere in which the temperaturewas kept at 25° C.).

Further, Table 10 shows the element characteristics of thelight-emitting elements 11 and 12 at around 1000 cd/m².

TABLE 10 Element characteristics of light-emitting elements of Example 5External Current Current quantum Voltage density Chromaticity Luminanceefficiency efficiency (V) (mA/cm²) (x, y) (cd/m²) (cd/A) (%) Light- 3.19.5 (0.14, 0.13) 1000 11 11 emitting element 11 Light- 2.8 0.88 (0.49,0.50) 1000 120 32 emitting element 12

FIG. 29 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 11. FIG. 32shows an emission spectrum when a current at a current density of 2.5mA/cm² was supplied to the light-emitting element 12. In each of FIG. 29and FIG. 32, the horizontal axis represents wavelength (nm) and thevertical axis represents emission intensity (an arbitrary unit). Asshown in FIG. 29, the emission spectrum of the light-emitting element 11has a peak in the blue wavelength region, which indicates that emissionfrom the light-emitting material included in the first light-emittinglayer 513 was obtained. As shown in FIG. 32, the emission spectrum ofthe light-emitting element 12 has a peak in the yellow wavelengthregion, which indicates that emission from the light-emitting materialincluded in the second light-emitting layer 514 was obtained.

The light-emitting elements 11 and 12 were subjected to reliabilitytests. FIG. 30 shows the test result of the light-emitting element 11,and FIG. 33 shows the test result of the light-emitting element 12. Ineach of FIG. 30 and FIG. 33, the vertical axis represents normalizedluminance (%) on the assumption that an initial luminance is 100%, andthe horizontal axis represents driving time (h) of the light-emittingelements. Note that in the reliability test, the light-emitting elements11 and 12 were each driven under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant. Asa result, the light-emitting element 11 kept approximately 90% of theinitial luminance until 130 hours had elapsed, and the light-emittingelement 12 kept approximately 90% of the initial luminance until 1300hours had elapsed.

The structures described in this example can be used in an appropriatecombination with any of the structures described in the otherembodiments and examples.

Reference Example

In this reference example, a method for synthesizingN,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPrn-03), an organic compound used in this example,is described. Note that a structure of 1,6BnfAPrn-03 is shown below.

Step 1: Synthesis of 6-iodobenzo[b]naphtho[1,2-d]furan

Into a 500 mL three-neck flask were put 8.5 g (39 mmol) ofbenzo[b]naphtho[1,2-d]furan, and the air in the flask was replaced withnitrogen. Then, 195 mL of tetrahydrofuran (THF) was added thereto. Thissolution was cooled to −75° C. Then, 25 mL (40 mmol) of n-butyllithium(a 1.59 mol/L n-hexane solution) was dropped into this solution. Afterthe drop, the resulting solution was stirred at room temperature for 1hour.

After a predetermined period of time, the resulting solution was cooledto −75° C. Then, a solution in which 10 g (40 mmol) of iodine had beendissolved in 40 mL of THF was dropped into this solution. After thedrop, the resulting solution was stirred for 17 hours while thetemperature of the solution was returned to room temperature. After apredetermined period of time, an aqueous solution of sodium thiosulfatewas added to the mixture, and the resulting mixture was stirred for 1hour. Then, an organic layer of the mixture was washed with water anddried with magnesium sulfate. After the drying, the mixture wasgravity-filtered to give a solution. The resulting solution wassuction-filtered through Celite (Catalog No. 531-16855 produced by WakoPure Chemical Industries, Ltd.) and Florisil (Catalog No. 540-00135produced by Wako Pure Chemical Industries, Ltd.) to give a filtrate. Theresulting filtrate was concentrated to give a solid. The resulting solidwas recrystallized from toluene to give 6.0 g (18 mmol) of white powderof the target substance in a yield of 45%. A synthetic scheme of Step 1is shown below.

Step 2: Synthesis of 6-phenylbenzo[b]naphtho[1,2-d]furan

Into a 200 mL three-neck flask were put 6.0 g (18 mmol) of6-iodobenzo[b]naphtho[1,2-d]furan, 2.4 g (19 mmol) of phenylboronicacid, 70 mL of toluene, 20 mL of ethanol, and 22 mL of an aqueoussolution of potassium carbonate (2.0 mol/L). The mixture was degassed bybeing stirred while the pressure was reduced. After the degassing, theair in the flask was replaced with nitrogen, and then 480 mg (0.42 mmol)of tetrakis(triphenylphosphine)palladium(0) was added to the mixture.The resulting mixture was stirred at 90° C. under a nitrogen stream for12 hours.

After a predetermined time has passed, water was added to the mixture,and the solution was separated into the aqueous layer and an organiclayer. An extracted solution which was extracted with toluene from theaqueous layer and the organic layer were combined, and the mixture waswashed with water and then dried with magnesium sulfate. The mixture wasgravity-filtered to give a filtrate. The resulting filtrate wasconcentrated to give a solid, and the resulting solid was dissolved intoluene. The resulting solution was suction-filtered through Celite(Catalog No. 531-16855 produced by Wako Pure Chemical Industries, Ltd.),Florisil (Catalog No. 540-00135 produced by Wako Pure ChemicalIndustries, Ltd.), and alumina to give a filtrate. The resultingfiltrate was concentrated to give a solid. The resulting solid wasrecrystallized from toluene to give a 4.9 g (17 mmol) of a white solidof the target substance in a yield of 93%. A synthetic scheme of Step 2is shown below.

Step 3: Synthesis of 8-iodo-6-phenylbenzo[b]naphtho[1,2-d]furan

Into a 300 mL three-neck flask was put 4.9 g (17 mmol) of6-phenylbenzo[b]naphtho[1,2-d]furan, and the air in the flask wasreplaced with nitrogen. Then, 87 mL of tetrahydrofuran (THY) was addedthereto. The resulting solution was cooled to −75° C. Then, 11 mL (18mmol) of n-butyllithium (a 1.59 mol/L n-hexane solution) was droppedinto the solution. After the drop, the resulting solution was stirred atroom temperature for 1 hour. After a predetermined period of time, theresulting solution was cooled to −75° C. Then, a solution in which 4.6 g(18 mmol) of iodine had been dissolved in 18 mL of THF was dropped intothe resulting solution.

The resulting solution was stirred for 17 hours while the temperature ofthe solution was returned to room temperature. After a predeterminedperiod of time, an aqueous solution of sodium thiosulfate was added tothe mixture, and the resulting mixture was stirred for 1 hour. Then, anorganic layer of the mixture was washed with water and dried withmagnesium sulfate. The mixture was gravity-filtered to give a filtrate.The resulting filtrate was suction-filtered through Celite (Catalog No.531-16855 produced by Wako Pure Chemical Industries, Ltd.), Florisil(Catalog No. 540-00135 produced by Wako Pure Chemical Industries, Ltd.),and alumina to give a filtrate. The resulting filtrate was concentratedto give a solid. The resulting solid was recrystallized from toluene togive 3.7 g (8.8 mmol) of a target white solid in a yield of 53%. Asynthesis scheme of Step 3 is shown below.

Step 4: Synthesis of 1,6BnfAPrn-03

Into a 100 mL three-neck flask were put 0.71 g (2.0 mmol) of1,6-dibromopyrene, 1.0 g (10.4 mmol) of sodium-tert-butoxide, 10 mL oftoluene, 0.36 mL (4.0 mmol) of aniline, and 0.3 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution), and the air in theflask was replaced with nitrogen. To this mixture was added 50 mg (85μmol) of bis(dibenzylideneacetone)palladium(0), and the resultingmixture was stirred at 80° C. for 2 hours.

After a predetermined period of time, to the resulting mixture wereadded 1.7 g (4.0 mmol) of 8-iodo-6-phenylbenzo[b]naphtho[1,2-d]furan,180 mg (0.44 mmol) of 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl(abbreviation: S-Phos), and 50 mg (85 μmol) ofbis(dibenzylideneacetone)palladium(0), and the resulting mixture wasstirred at 100° C. for 15 hours. After a predetermined period of time,the resulting mixture was filtered through Celite (Catalog No. 531-16855produced by Wako Pure Chemical Industries, Ltd.) to give a filtrate. Theobtained filtrate was concentrated to give a solid. The resulting solidwas washed with ethanol and recrystallized from toluene to give 1.38 g(1.4 mmol) of a yellow solid of the target substance in a yield of 71%.

By a train sublimation method, 1.37 mg (1.4 mmol) of the resultingyellow solid was purified by sublimation. The purification bysublimation was performed by heating the yellow solid at 370° C. at anargon flow rate of 10 mL/min under a pressure of 2.3 Pa. As a result ofthe purification by sublimation, 0.68 g (0.70 mmol) of the yellow solidwas obtained in a collection rate of 50%. A synthesis scheme of Step 4is shown below.

An analysis result by nuclear magnetic resonance (¹H-NMR) spectroscopyof the yellow solid obtained in Step 4 is described below. The resultrevealed that 1,6BnfAPrn-03 was obtained.

¹H-NMR (dichloromethane-d2, 500 MHz): δ=6.88 (t, J=7.7 Hz, 4H),7.03-7.06 (m, 6H), 7.11 (t, J=7.5 Hz, 2H), 7.13 (d, J=8.0 Hz, 2H),7.28-7.32 (m, 8H), 7.37 (t, J=8.0 Hz, 2H), 7.59 (t, J=7.2 Hz, 2H), 7.75(t, J=7.7 Hz, 2H), 7.84 (d, J=9.0 Hz, 2H), 7.88 (d, J=8.0 Hz, 2H), 8.01(s, 2H), 8.07 (d, J=8.0 Hz, 4H), 8.14 (d, J=9.0 Hz, 2H), 8.21 (d, J=8.0Hz, 2H), 8.69 (d, J=8.5 Hz, 2H).

REFERENCE NUMERALS

-   100: light-emitting element, 101: electrode, 102: electrode, 111:    hole-injection layer, 112: hole-transport layer, 113: light-emitting    layer, 114: light-emitting layer, 115: electron-transport layer,    116: electron-injection layer, 120: separation layer, 130: EL layer,    131: light-emitting unit, 132: light-emitting unit, 133: charge    generation layer, 140: light-emitting element, 150: light-emitting    element, 160: light-emitting element, 170: light-emitting element,    500: glass substrate, 501: electrode, 502: electrode, 511:    hole-injection layer, 512: hole-transport layer, 513: light-emitting    layer, 514: light-emitting layer, 515(1): electron-transport layer,    515(2): electron-transport layer, 516: electron-injection layer,    520: separation layer, 550: sealing substrate, 552: coloring layer,    600: light-emitting device, 601: source line driver circuit portion,    602: pixel portion, 603: gate line driver circuit portion, 604:    sealing substrate, 605: sealing member, 607: region, 608: wiring,    609: FPC, 610: element substrate, 611: FET, 612: FET, 613:    electrode, 614: insulator, 616: EL layer, 617: electrode, 618:    light-emitting element, 623: FET, 624: FET, 801: pixel circuit, 802:    pixel portion, 804: driver circuit portion, 804 a: gate driver, 804    b: source driver, 806: protection circuit, 807: terminal portion,    852: transistor, 854: transistor, 862: capacitor, 872:    light-emitting element, 1001: substrate, 1002: base insulating film,    1003: gate insulating film, 1006: gate electrode, 1007: gate    electrode, 1008: gate electrode, 1020: interlayer insulating film,    1021: interlayer insulating film, 1022: electrode, 1024B: electrode,    1024G: electrode, 1024R: electrode, 1024Y: electrode, 1025:    partition, 1026: electrode, 1028: EL layer, 1031: sealing substrate,    1032: sealing member, 1033: base material, 1034B: coloring layer,    1034G: coloring layer, 1034R: coloring layer, 1034Y: coloring layer,    1035: black layer, 1036: overcoat layer, 1037: interlayer insulating    film, 1040: pixel portion, 1041: driver circuit portion, 1042:    peripheral portion, 8000: display module, 8001: upper cover, 8002:    lower cover, 8003: FPC, 8004: touch panel, 8005: FPC, 8006: display    panel, 8009: frame, 8010: printed board, 8011: battery, 8501:    lighting device, 8502: lighting device, 8503: lighting device, 8504:    lighting device, 9000: housing, 9001: display portion, 9003:    speaker, 9005: operation key, 9006: connection terminal, 9007:    sensor, 9008: microphone, 9050: operation button, 9051: information,    9052: information, 9053: information, 9054: information, 9055:    hinge, 9100: portable information terminal, 9101: portable    information terminal, 9102: portable information terminal, 9200:    portable information terminal, 9201: portable information terminal.

This application is based on Japanese Patent Application serial no.2014-112448 filed with Japan Patent Office on May 30, 2014 and JapanesePatent Application serial no. 2014-241137 filed with Japan Patent Officeon Nov. 28, 2014, the entire contents of which are hereby incorporatedby reference.

The invention claimed is:
 1. A light-emitting element comprising: afirst electrode; a second electrode; and an electroluminescence layerbetween the first electrode and the second electrode, wherein theelectroluminescence layer comprises a first light-emitting layer and asecond light-emitting layer, wherein the first light-emitting layercomprises a fluorescent material and a host material, wherein the secondlight-emitting layer comprises a phosphorescent material, a firstorganic compound, and a second organic compound, wherein the firstorganic compound and the second organic compound form an exciplex,wherein energy is transferred from the exciplex to the phosphorescentmaterial, and wherein a triplet excited level of the host material islower than triplet excited levels of the first organic compound and thesecond organic compound.
 2. The light-emitting element according toclaim 1, wherein a singlet excited level of the host material is higherthan a singlet excited level of the fluorescent material, and wherein atriplet excited level of the host material is lower than a tripletexcited level of the fluorescent material.
 3. The light-emitting elementaccording to claim 1, wherein the first light-emitting layer and thesecond light-emitting layer are in contact with each other.
 4. Thelight-emitting element according to claim 1, wherein the firstlight-emitting layer and the second light-emitting layer are spaced fromeach other.
 5. The light-emitting element according to claim 4, whereina layer in which a hole-transport material and an electron-transportmaterial are mixed is located between the first light-emitting layer andthe second light-emitting layer.
 6. The light-emitting element accordingto claim 1, wherein the first electrode is an anode, wherein the secondelectrode is a cathode, wherein the first light-emitting layer is overthe first electrode, and wherein the second light-emitting layer is overthe first light-emitting layer.
 7. A light-emitting device comprising:the light-emitting element according to claim 1; and a transistor or asubstrate.
 8. A module comprising: the light-emitting device accordingto claim 7; and a connector connected to the light-emitting device. 9.An electronic device comprising: the light-emitting device according toclaim 7; and any of an external connection port, a keyboard, anoperation button, a speaker and a microphone.
 10. A lighting devicecomprising: the light-emitting device according to claim 7; and ahousing.
 11. A light-emitting element comprising: a first electrode; asecond electrode; and an electroluminescence layer between the firstelectrode and the second electrode, wherein the electroluminescencelayer comprises a first light-emitting layer and a second light-emittinglayer, wherein the first light-emitting layer comprises a fluorescentmaterial and a host material, wherein the second light-emitting layercomprises a phosphorescent material, a first organic compound, and asecond organic compound, wherein an emission spectrum of the secondlight-emitting layer has a peak in a wavelength region of greater thanor equal to 550 nm and less than or equal to 590 nm, wherein the firstorganic compound and the second organic compound form an exciplex,wherein energy is transferred from the exciplex to the phosphorescentmaterial, and wherein a triplet excited level of the host material islower than triplet excited levels of the first organic compound and thesecond organic compound.
 12. The light-emitting element according toclaim 11, wherein a singlet excited level of the host material is higherthan a singlet excited level of the fluorescent material, and wherein atriplet excited level of the host material is lower than a tripletexcited level of the fluorescent material.
 13. The light-emittingelement according to claim 11, wherein the first light-emitting layerand the second light-emitting layer are in contact with each other. 14.The light-emitting element according to claim 11, wherein the firstlight-emitting layer and the second light-emitting layer are spaced fromeach other.
 15. The light-emitting element according to claim 14,wherein a layer in which a hole-transport material and anelectron-transport material are mixed is located between the firstlight-emitting layer and the second light-emitting layer.
 16. Thelight-emitting element according to claim 11, wherein the firstelectrode is an anode, wherein the second electrode is a cathode,wherein the first light-emitting layer is over the first electrode, andwherein the second light-emitting layer is over the first light-emittinglayer.
 17. A light-emitting element comprising: a first electrode; asecond electrode; and an electroluminescence layer between the firstelectrode and the second electrode, wherein the electroluminescencelayer comprises a first light-emitting layer and a second light-emittinglayer, wherein the first light-emitting layer comprises a fluorescentmaterial and a host material, wherein the second light-emitting layercomprises a phosphorescent material, a first organic compound, and asecond organic compound, wherein the first organic compound and thesecond organic compound form an exciplex, wherein an emission spectrumof the phosphorescent material has a peak in a wavelength region ofgreater than or equal to 550 nm and less than or equal to 590 nm,wherein energy is transferred from the exciplex to the phosphorescentmaterial, and wherein a triplet excited level of the host material islower than triplet excited levels of the first organic compound and thesecond organic compound.
 18. The light-emitting element according toclaim 17, wherein a singlet excited level of the host material is higherthan a singlet excited level of the fluorescent material, and wherein atriplet excited level of the host material is lower than a tripletexcited level of the fluorescent material.
 19. The light-emittingelement according to claim 17, wherein the first light-emitting layerand the second light-emitting layer are in contact with each other. 20.The light-emitting element according to claim 17, wherein the firstlight-emitting layer and the second light-emitting layer are spaced fromeach other.
 21. The light-emitting element according to claim 20,wherein a layer in which a hole-transport material and anelectron-transport material are mixed is located between the firstlight-emitting layer and the second light-emitting layer.
 22. Thelight-emitting element according to claim 17, wherein the firstelectrode is an anode, wherein the second electrode is a cathode,wherein the first light-emitting layer is over the first electrode, andwherein the second light-emitting layer is over the first light-emittinglayer.